diff --git a/polkadot/api/src/full.rs b/polkadot/api/src/full.rs
index 6b3035e5da..7c39bc3c6c 100644
--- a/polkadot/api/src/full.rs
+++ b/polkadot/api/src/full.rs
@@ -20,7 +20,7 @@ use client::backend::{Backend, LocalBackend};
 use client::block_builder::BlockBuilder as ClientBlockBuilder;
 use client::{Client, LocalCallExecutor};
 use polkadot_executor::Executor as LocalDispatch;
-use substrate_executor::{NativeExecutionDispatch, NativeExecutor};
+use substrate_executor::NativeExecutor;
 use state_machine;
 
 use runtime::Address;
@@ -28,23 +28,13 @@ use runtime_primitives::traits::AuxLookup;
 use primitives::{AccountId, Block, Header, BlockId, Hash, Index, SessionKey, Timestamp, UncheckedExtrinsic};
 use primitives::parachain::{CandidateReceipt, DutyRoster, Id as ParaId};
 
-use {CheckedBlockId, BlockBuilder, PolkadotApi, LocalPolkadotApi, ErrorKind, Error, Result};
-
-/// A checked block ID used for the substrate-client implementation of CheckedBlockId;
-#[derive(Debug, Clone, Copy)]
-pub struct CheckedId(pub(crate) BlockId);
-
-impl CheckedBlockId for CheckedId {
-	fn block_id(&self) -> &BlockId {
-		&self.0
-	}
-}
+use {BlockBuilder, PolkadotApi, LocalPolkadotApi, ErrorKind, Error, Result};
 
 // set up the necessary scaffolding to execute a set of calls to the runtime.
 // this creates a new block on top of the given ID and initialises it.
 macro_rules! with_runtime {
 	($client: ident, $at: expr, $exec: expr) => {{
-		let parent = $at.block_id();
+		let parent = $at;
 		let header = Header {
 			parent_hash: $client.block_hash_from_id(&parent)?
 				.ok_or_else(|| ErrorKind::UnknownBlock(format!("{:?}", parent)))?,
@@ -83,39 +73,29 @@ impl<B: LocalBackend<Block>> BlockBuilder for ClientBlockBuilder<B, LocalCallExe
 impl<B: LocalBackend<Block>> PolkadotApi for Client<B, LocalCallExecutor<B, NativeExecutor<LocalDispatch>>, Block>
 	where ::client::error::Error: From<<<B as Backend<Block>>::State as state_machine::backend::Backend>::Error>
 {
-	type CheckedBlockId = CheckedId;
 	type BlockBuilder = ClientBlockBuilder<B, LocalCallExecutor<B, NativeExecutor<LocalDispatch>>, Block>;
 
-	fn check_id(&self, id: BlockId) -> Result<CheckedId> {
-		// bail if the code is not the same as the natively linked.
-		if self.code_at(&id.into())? != LocalDispatch::native_equivalent() {
-			bail!("This node is out of date. Block authoring may not work correctly. Bailing.")
-		}
-
-		Ok(CheckedId(id))
-	}
-
-	fn session_keys(&self, at: &CheckedId) -> Result<Vec<SessionKey>> {
+	fn session_keys(&self, at: &BlockId) -> Result<Vec<SessionKey>> {
 		with_runtime!(self, at, ::runtime::Consensus::authorities)
 	}
 
-	fn validators(&self, at: &CheckedId) -> Result<Vec<AccountId>> {
+	fn validators(&self, at: &BlockId) -> Result<Vec<AccountId>> {
 		with_runtime!(self, at, ::runtime::Session::validators)
 	}
 
-	fn random_seed(&self, at: &CheckedId) -> Result<Hash> {
+	fn random_seed(&self, at: &BlockId) -> Result<Hash> {
 		with_runtime!(self, at, ::runtime::System::random_seed)
 	}
 
-	fn duty_roster(&self, at: &CheckedId) -> Result<DutyRoster> {
+	fn duty_roster(&self, at: &BlockId) -> Result<DutyRoster> {
 		with_runtime!(self, at, ::runtime::Parachains::calculate_duty_roster)
 	}
 
-	fn timestamp(&self, at: &CheckedId) -> Result<Timestamp> {
+	fn timestamp(&self, at: &BlockId) -> Result<Timestamp> {
 		with_runtime!(self, at, ::runtime::Timestamp::get)
 	}
 
-	fn evaluate_block(&self, at: &CheckedId, block: Block) -> Result<bool> {
+	fn evaluate_block(&self, at: &BlockId, block: Block) -> Result<bool> {
 		use substrate_executor::error::ErrorKind as ExecErrorKind;
 		use codec::Slicable;
 		use runtime::Block as RuntimeBlock;
@@ -136,28 +116,28 @@ impl<B: LocalBackend<Block>> PolkadotApi for Client<B, LocalCallExecutor<B, Nati
 		}
 	}
 
-	fn index(&self, at: &CheckedId, account: AccountId) -> Result<Index> {
+	fn index(&self, at: &BlockId, account: AccountId) -> Result<Index> {
 		with_runtime!(self, at, || ::runtime::System::account_nonce(account))
 	}
 
-	fn lookup(&self, at: &Self::CheckedBlockId, address: Address) -> Result<Option<AccountId>> {
+	fn lookup(&self, at: &BlockId, address: Address) -> Result<Option<AccountId>> {
 		with_runtime!(self, at, || <::runtime::Staking as AuxLookup>::lookup(address).ok())
 	}
 
-	fn active_parachains(&self, at: &CheckedId) -> Result<Vec<ParaId>> {
+	fn active_parachains(&self, at: &BlockId) -> Result<Vec<ParaId>> {
 		with_runtime!(self, at, ::runtime::Parachains::active_parachains)
 	}
 
-	fn parachain_code(&self, at: &CheckedId, parachain: ParaId) -> Result<Option<Vec<u8>>> {
+	fn parachain_code(&self, at: &BlockId, parachain: ParaId) -> Result<Option<Vec<u8>>> {
 		with_runtime!(self, at, || ::runtime::Parachains::parachain_code(parachain))
 	}
 
-	fn parachain_head(&self, at: &CheckedId, parachain: ParaId) -> Result<Option<Vec<u8>>> {
+	fn parachain_head(&self, at: &BlockId, parachain: ParaId) -> Result<Option<Vec<u8>>> {
 		with_runtime!(self, at, || ::runtime::Parachains::parachain_head(parachain))
 	}
 
-	fn build_block(&self, at: &CheckedId, timestamp: Timestamp, new_heads: Vec<CandidateReceipt>) -> Result<Self::BlockBuilder> {
-		let mut block_builder = self.new_block_at(at.block_id())?;
+	fn build_block(&self, at: &BlockId, timestamp: Timestamp, new_heads: Vec<CandidateReceipt>) -> Result<Self::BlockBuilder> {
+		let mut block_builder = self.new_block_at(at)?;
 		for inherent in self.inherent_extrinsics(at, timestamp, new_heads)? {
 			block_builder.push(inherent)?;
 		}
@@ -165,7 +145,7 @@ impl<B: LocalBackend<Block>> PolkadotApi for Client<B, LocalCallExecutor<B, Nati
 		Ok(block_builder)
 	}
 
-	fn inherent_extrinsics(&self, at: &Self::CheckedBlockId, timestamp: Timestamp, new_heads: Vec<CandidateReceipt>) -> Result<Vec<UncheckedExtrinsic>> {
+	fn inherent_extrinsics(&self, at: &BlockId, timestamp: Timestamp, new_heads: Vec<CandidateReceipt>) -> Result<Vec<UncheckedExtrinsic>> {
 		use codec::Slicable;
 
 		with_runtime!(self, at, || {
@@ -231,7 +211,7 @@ mod tests {
 	#[test]
 	fn gets_session_and_validator_keys() {
 		let client = client();
-		let id = client.check_id(BlockId::number(0)).unwrap();
+		let id = BlockId::number(0);
 		assert_eq!(client.session_keys(&id).unwrap(), session_keys());
 		assert_eq!(client.validators(&id).unwrap(), validators());
 	}
@@ -240,7 +220,7 @@ mod tests {
 	fn build_block_implicit_succeeds() {
 		let client = client();
 
-		let id = client.check_id(BlockId::number(0)).unwrap();
+		let id = BlockId::number(0);
 		let block_builder = client.build_block(&id, 1_000_000, Vec::new()).unwrap();
 		let block = block_builder.bake().unwrap();
 
@@ -252,10 +232,10 @@ mod tests {
 	fn build_block_with_inherent_succeeds() {
 		let client = client();
 
-		let id = client.check_id(BlockId::number(0)).unwrap();
+		let id = BlockId::number(0);
 		let inherent = client.inherent_extrinsics(&id, 1_000_000, Vec::new()).unwrap();
 
-		let mut block_builder = client.new_block_at(id.block_id()).unwrap();
+		let mut block_builder = client.new_block_at(&id).unwrap();
 		for extrinsic in inherent {
 			block_builder.push(extrinsic).unwrap();
 		}
@@ -266,16 +246,11 @@ mod tests {
 		assert!(block.header.extrinsics_root != Default::default());
 	}
 
-	#[test]
-	fn fails_to_check_id_for_unknown_block() {
-		assert!(client().check_id(BlockId::number(100)).is_err());
-	}
-
 	#[test]
 	fn gets_random_seed_with_genesis() {
 		let client = client();
 
-		let id = client.check_id(BlockId::number(0)).unwrap();
+		let id = BlockId::number(0);
 		assert!(client.random_seed(&id).is_ok());
 	}
 }
diff --git a/polkadot/api/src/lib.rs b/polkadot/api/src/lib.rs
index 81e3b02420..27bea18a0d 100644
--- a/polkadot/api/src/lib.rs
+++ b/polkadot/api/src/lib.rs
@@ -77,12 +77,6 @@ impl From<client::error::Error> for Error {
 	}
 }
 
-/// A checked block identifier.
-pub trait CheckedBlockId: Clone + 'static {
-	/// Yield the underlying block ID.
-	fn block_id(&self) -> &BlockId;
-}
-
 /// Build new blocks.
 pub trait BlockBuilder {
 	/// Push an extrinsic onto the block. Fails if the extrinsic is invalid.
@@ -96,57 +90,49 @@ pub trait BlockBuilder {
 ///
 /// All calls should fail when the exact runtime is unknown.
 pub trait PolkadotApi {
-	/// A checked block ID. Used to avoid redundancy of code check.
-	type CheckedBlockId: CheckedBlockId;
 	/// The block builder for this API type.
 	type BlockBuilder: BlockBuilder;
 
-	/// Check whether requests at the given block ID can be served.
-	///
-	/// It should not be possible to instantiate this type without going
-	/// through this function.
-	fn check_id(&self, id: BlockId) -> Result<Self::CheckedBlockId>;
-
 	/// Get session keys at a given block.
-	fn session_keys(&self, at: &Self::CheckedBlockId) -> Result<Vec<SessionKey>>;
+	fn session_keys(&self, at: &BlockId) -> Result<Vec<SessionKey>>;
 
 	/// Get validators at a given block.
-	fn validators(&self, at: &Self::CheckedBlockId) -> Result<Vec<AccountId>>;
+	fn validators(&self, at: &BlockId) -> Result<Vec<AccountId>>;
 
 	/// Get the value of the randomness beacon at a given block.
-	fn random_seed(&self, at: &Self::CheckedBlockId) -> Result<Hash>;
+	fn random_seed(&self, at: &BlockId) -> Result<Hash>;
 
 	/// Get the authority duty roster at a block.
-	fn duty_roster(&self, at: &Self::CheckedBlockId) -> Result<DutyRoster>;
+	fn duty_roster(&self, at: &BlockId) -> Result<DutyRoster>;
 
 	/// Get the timestamp registered at a block.
-	fn timestamp(&self, at: &Self::CheckedBlockId) -> Result<Timestamp>;
+	fn timestamp(&self, at: &BlockId) -> Result<Timestamp>;
 
 	/// Get the nonce (né index) of an account at a block.
-	fn index(&self, at: &Self::CheckedBlockId, account: AccountId) -> Result<Index>;
+	fn index(&self, at: &BlockId, account: AccountId) -> Result<Index>;
 
 	/// Get the account id of an address at a block.
-	fn lookup(&self, at: &Self::CheckedBlockId, address: Address) -> Result<Option<AccountId>>;
+	fn lookup(&self, at: &BlockId, address: Address) -> Result<Option<AccountId>>;
 
 	/// Get the active parachains at a block.
-	fn active_parachains(&self, at: &Self::CheckedBlockId) -> Result<Vec<ParaId>>;
+	fn active_parachains(&self, at: &BlockId) -> Result<Vec<ParaId>>;
 
 	/// Get the validation code of a parachain at a block. If the parachain is active, this will always return `Some`.
-	fn parachain_code(&self, at: &Self::CheckedBlockId, parachain: ParaId) -> Result<Option<Vec<u8>>>;
+	fn parachain_code(&self, at: &BlockId, parachain: ParaId) -> Result<Option<Vec<u8>>>;
 
 	/// Get the chain head of a parachain. If the parachain is active, this will always return `Some`.
-	fn parachain_head(&self, at: &Self::CheckedBlockId, parachain: ParaId) -> Result<Option<Vec<u8>>>;
+	fn parachain_head(&self, at: &BlockId, parachain: ParaId) -> Result<Option<Vec<u8>>>;
 
 	/// Evaluate a block. Returns true if the block is good, false if it is known to be bad,
 	/// and an error if we can't evaluate for some reason.
-	fn evaluate_block(&self, at: &Self::CheckedBlockId, block: Block) -> Result<bool>;
+	fn evaluate_block(&self, at: &BlockId, block: Block) -> Result<bool>;
 
 	/// Build a block on top of the given, with inherent extrinsics pre-pushed.
-	fn build_block(&self, at: &Self::CheckedBlockId, timestamp: Timestamp, new_heads: Vec<CandidateReceipt>) -> Result<Self::BlockBuilder>;
+	fn build_block(&self, at: &BlockId, timestamp: Timestamp, new_heads: Vec<CandidateReceipt>) -> Result<Self::BlockBuilder>;
 
 	/// Attempt to produce the (encoded) inherent extrinsics for a block being built upon the given.
 	/// This may vary by runtime and will fail if a runtime doesn't follow the same API.
-	fn inherent_extrinsics(&self, at: &Self::CheckedBlockId, timestamp: Timestamp, new_heads: Vec<CandidateReceipt>) -> Result<Vec<UncheckedExtrinsic>>;
+	fn inherent_extrinsics(&self, at: &BlockId, timestamp: Timestamp, new_heads: Vec<CandidateReceipt>) -> Result<Vec<UncheckedExtrinsic>>;
 }
 
 /// Mark for all Polkadot API implementations, that are making use of state data, stored locally.
diff --git a/polkadot/api/src/light.rs b/polkadot/api/src/light.rs
index 6a4f1f0322..e20c1a245e 100644
--- a/polkadot/api/src/light.rs
+++ b/polkadot/api/src/light.rs
@@ -24,8 +24,7 @@ use state_machine;
 use primitives::{AccountId, Block, BlockId, Hash, Index, SessionKey, Timestamp, UncheckedExtrinsic};
 use runtime::Address;
 use primitives::parachain::{CandidateReceipt, DutyRoster, Id as ParaId};
-use full::CheckedId;
-use {PolkadotApi, BlockBuilder, RemotePolkadotApi, CheckedBlockId, Result, ErrorKind};
+use {PolkadotApi, BlockBuilder, RemotePolkadotApi, Result, ErrorKind};
 
 /// Light block builder. TODO: make this work (efficiently)
 #[derive(Clone, Copy)]
@@ -47,65 +46,60 @@ pub struct RemotePolkadotApiWrapper<B: Backend<Block>, E: CallExecutor<Block>>(p
 impl<B: Backend<Block>, E: CallExecutor<Block>> PolkadotApi for RemotePolkadotApiWrapper<B, E>
 	where ::client::error::Error: From<<<B as Backend<Block>>::State as state_machine::backend::Backend>::Error>
 {
-	type CheckedBlockId = CheckedId;
 	type BlockBuilder = LightBlockBuilder;
 
-	fn check_id(&self, id: BlockId) -> Result<CheckedId> {
-		Ok(CheckedId(id))
-	}
-
-	fn session_keys(&self, at: &CheckedId) -> Result<Vec<SessionKey>> {
-		self.0.executor().call(at.block_id(), "authorities", &[])
+	fn session_keys(&self, at: &BlockId) -> Result<Vec<SessionKey>> {
+		self.0.executor().call(at, "authorities", &[])
 			.and_then(|r| Vec::<SessionKey>::decode(&mut &r.return_data[..])
 				.ok_or("error decoding session keys".into()))
 			.map_err(Into::into)
 	}
 
-	fn validators(&self, _at: &CheckedId) -> Result<Vec<AccountId>> {
+	fn validators(&self, _at: &BlockId) -> Result<Vec<AccountId>> {
 		Err(ErrorKind::UnknownRuntime.into())
 	}
 
-	fn random_seed(&self, _at: &Self::CheckedBlockId) -> Result<Hash> {
+	fn random_seed(&self, _at: &BlockId) -> Result<Hash> {
 		Err(ErrorKind::UnknownRuntime.into())
 	}
 
-	fn duty_roster(&self, _at: &CheckedId) -> Result<DutyRoster> {
+	fn duty_roster(&self, _at: &BlockId) -> Result<DutyRoster> {
 		Err(ErrorKind::UnknownRuntime.into())
 	}
 
-	fn timestamp(&self, _at: &CheckedId) -> Result<Timestamp> {
+	fn timestamp(&self, _at: &BlockId) -> Result<Timestamp> {
 		Err(ErrorKind::UnknownRuntime.into())
 	}
 
-	fn evaluate_block(&self, _at: &CheckedId, _block: Block) -> Result<bool> {
+	fn evaluate_block(&self, _at: &BlockId, _block: Block) -> Result<bool> {
 		Err(ErrorKind::UnknownRuntime.into())
 	}
 
-	fn index(&self, _at: &CheckedId, _account: AccountId) -> Result<Index> {
+	fn index(&self, _at: &BlockId, _account: AccountId) -> Result<Index> {
 		Err(ErrorKind::UnknownRuntime.into())
 	}
 
-	fn lookup(&self, _at: &CheckedId, _address: Address) -> Result<Option<AccountId>> {
+	fn lookup(&self, _at: &BlockId, _address: Address) -> Result<Option<AccountId>> {
 		Err(ErrorKind::UnknownRuntime.into())
 	}
 
-	fn active_parachains(&self, _at: &Self::CheckedBlockId) -> Result<Vec<ParaId>> {
+	fn active_parachains(&self, _at: &BlockId) -> Result<Vec<ParaId>> {
 		Err(ErrorKind::UnknownRuntime.into())
 	}
 
-	fn parachain_code(&self, _at: &Self::CheckedBlockId, _parachain: ParaId) -> Result<Option<Vec<u8>>> {
+	fn parachain_code(&self, _at: &BlockId, _parachain: ParaId) -> Result<Option<Vec<u8>>> {
 		Err(ErrorKind::UnknownRuntime.into())
 	}
 
-	fn parachain_head(&self, _at: &Self::CheckedBlockId, _parachain: ParaId) -> Result<Option<Vec<u8>>> {
+	fn parachain_head(&self, _at: &BlockId, _parachain: ParaId) -> Result<Option<Vec<u8>>> {
 		Err(ErrorKind::UnknownRuntime.into())
 	}
 
-	fn build_block(&self, _at: &Self::CheckedBlockId, _timestamp: Timestamp, _new_heads: Vec<CandidateReceipt>) -> Result<Self::BlockBuilder> {
+	fn build_block(&self, _at: &BlockId, _timestamp: Timestamp, _new_heads: Vec<CandidateReceipt>) -> Result<Self::BlockBuilder> {
 		Err(ErrorKind::UnknownRuntime.into())
 	}
 
-	fn inherent_extrinsics(&self, _at: &Self::CheckedBlockId, _timestamp: Timestamp, _new_heads: Vec<CandidateReceipt>) -> Result<Vec<Vec<u8>>> {
+	fn inherent_extrinsics(&self, _at: &BlockId, _timestamp: Timestamp, _new_heads: Vec<CandidateReceipt>) -> Result<Vec<Vec<u8>>> {
 		Err(ErrorKind::UnknownRuntime.into())
 	}
 }
diff --git a/polkadot/consensus/src/collation.rs b/polkadot/consensus/src/collation.rs
index 3738ae9004..f0b1f626c6 100644
--- a/polkadot/consensus/src/collation.rs
+++ b/polkadot/consensus/src/collation.rs
@@ -22,7 +22,7 @@
 use std::sync::Arc;
 
 use polkadot_api::PolkadotApi;
-use polkadot_primitives::{Hash, AccountId};
+use polkadot_primitives::{Hash, AccountId, BlockId};
 use polkadot_primitives::parachain::{Id as ParaId, Chain, BlockData, Extrinsic, CandidateReceipt};
 
 use futures::prelude::*;
@@ -57,7 +57,7 @@ pub trait Collators: Clone {
 pub struct CollationFetch<C: Collators, P: PolkadotApi> {
 	parachain: Option<ParaId>,
 	relay_parent_hash: Hash,
-	relay_parent: P::CheckedBlockId,
+	relay_parent: BlockId,
 	collators: C,
 	live_fetch: Option<<C::Collation as IntoFuture>::Future>,
 	client: Arc<P>,
@@ -65,7 +65,7 @@ pub struct CollationFetch<C: Collators, P: PolkadotApi> {
 
 impl<C: Collators, P: PolkadotApi> CollationFetch<C, P> {
 	/// Create a new collation fetcher for the given chain.
-	pub fn new(parachain: Chain, relay_parent: P::CheckedBlockId, relay_parent_hash: Hash, collators: C, client: Arc<P>) -> Self {
+	pub fn new(parachain: Chain, relay_parent: BlockId, relay_parent_hash: Hash, collators: C, client: Arc<P>) -> Self {
 		CollationFetch {
 			relay_parent_hash,
 			relay_parent,
@@ -145,7 +145,7 @@ error_chain! {
 }
 
 /// Check whether a given collation is valid. Returns `Ok`  on success, error otherwise.
-pub fn validate_collation<P: PolkadotApi>(client: &P, relay_parent: &P::CheckedBlockId, collation: &Collation) -> Result<(), Error> {
+pub fn validate_collation<P: PolkadotApi>(client: &P, relay_parent: &BlockId, collation: &Collation) -> Result<(), Error> {
 	use parachain::{self, ValidationParams};
 
 	let para_id = collation.receipt.parachain_index;
diff --git a/polkadot/consensus/src/lib.rs b/polkadot/consensus/src/lib.rs
index 4fb8fc4090..c75d8ac6ee 100644
--- a/polkadot/consensus/src/lib.rs
+++ b/polkadot/consensus/src/lib.rs
@@ -240,7 +240,6 @@ pub struct ProposerFactory<C, N, P> {
 impl<C, N, P> bft::ProposerFactory<Block> for ProposerFactory<C, N, P>
 	where
 		C: PolkadotApi + Send + Sync,
-		C::CheckedBlockId: Sync,
 		N: Network,
 		P: Collators,
 {
@@ -254,9 +253,9 @@ impl<C, N, P> bft::ProposerFactory<Block> for ProposerFactory<C, N, P>
 
 		let parent_hash = parent_header.blake2_256().into();
 
-		let checked_id = self.client.check_id(BlockId::hash(parent_hash))?;
-		let duty_roster = self.client.duty_roster(&checked_id)?;
-		let random_seed = self.client.random_seed(&checked_id)?;
+		let id = BlockId::hash(parent_hash);
+		let duty_roster = self.client.duty_roster(&id)?;
+		let random_seed = self.client.random_seed(&id)?;
 
 		let (group_info, local_duty) = make_group_info(
 			duty_roster,
@@ -264,7 +263,7 @@ impl<C, N, P> bft::ProposerFactory<Block> for ProposerFactory<C, N, P>
 			sign_with.public().into(),
 		)?;
 
-		let active_parachains = self.client.active_parachains(&checked_id)?;
+		let active_parachains = self.client.active_parachains(&id)?;
 
 		let n_parachains = active_parachains.len();
 		let table = Arc::new(SharedTable::new(group_info, sign_with.clone(), parent_hash));
@@ -291,7 +290,7 @@ impl<C, N, P> bft::ProposerFactory<Block> for ProposerFactory<C, N, P>
 			local_duty,
 			local_key: sign_with,
 			parent_hash,
-			parent_id: checked_id,
+			parent_id: id,
 			parent_number: parent_header.number,
 			random_seed,
 			router,
@@ -315,7 +314,7 @@ pub struct Proposer<C: PolkadotApi, R, P> {
 	local_duty: LocalDuty,
 	local_key: Arc<ed25519::Pair>,
 	parent_hash: Hash,
-	parent_id: C::CheckedBlockId,
+	parent_id: BlockId,
 	parent_number: BlockNumber,
 	random_seed: Hash,
 	router: R,
@@ -326,7 +325,6 @@ pub struct Proposer<C: PolkadotApi, R, P> {
 impl<C, R, P> bft::Proposer<Block> for Proposer<C, R, P>
 	where
 		C: PolkadotApi + Send + Sync,
-		C::CheckedBlockId: Sync,
 		R: TableRouter,
 		P: Collators,
 {
@@ -621,7 +619,7 @@ impl ProposalTiming {
 pub struct CreateProposal<C: PolkadotApi, R, P: Collators>  {
 	parent_hash: Hash,
 	parent_number: BlockNumber,
-	parent_id: C::CheckedBlockId,
+	parent_id: BlockId,
 	client: Arc<C>,
 	transaction_pool: Arc<TransactionPool<C>>,
 	collation: CollationFetch<P, C>,
diff --git a/polkadot/consensus/src/service.rs b/polkadot/consensus/src/service.rs
index f761c51d01..494e785809 100644
--- a/polkadot/consensus/src/service.rs
+++ b/polkadot/consensus/src/service.rs
@@ -242,7 +242,6 @@ impl Service {
 		where
 			A: LocalPolkadotApi + Send + Sync + 'static,
 			C: BlockchainEvents<Block> + ChainHead<Block> + bft::BlockImport<Block> + bft::Authorities<Block> + Send + Sync + 'static,
-			A::CheckedBlockId: Sync,
 	{
 		let (signal, exit) = ::exit_future::signal();
 		let thread = thread::spawn(move || {
diff --git a/polkadot/executor/src/lib.rs b/polkadot/executor/src/lib.rs
index be44d8afba..82cd5cd478 100644
--- a/polkadot/executor/src/lib.rs
+++ b/polkadot/executor/src/lib.rs
@@ -20,4 +20,4 @@
 extern crate polkadot_runtime;
 #[macro_use] extern crate substrate_executor;
 
-native_executor_instance!(pub Executor, polkadot_runtime::api::dispatch, include_bytes!("../../runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.compact.wasm"));
+native_executor_instance!(pub Executor, polkadot_runtime::api::dispatch, polkadot_runtime::VERSION, include_bytes!("../../runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.compact.wasm"));
diff --git a/polkadot/runtime/Cargo.toml b/polkadot/runtime/Cargo.toml
index 9ac1f50175..4068595601 100644
--- a/polkadot/runtime/Cargo.toml
+++ b/polkadot/runtime/Cargo.toml
@@ -26,6 +26,7 @@ substrate-runtime-session = { path = "../../substrate/runtime/session" }
 substrate-runtime-staking = { path = "../../substrate/runtime/staking" }
 substrate-runtime-system = { path = "../../substrate/runtime/system" }
 substrate-runtime-timestamp = { path = "../../substrate/runtime/timestamp" }
+substrate-runtime-version = { path = "../../substrate/runtime/version" }
 
 [dev-dependencies]
 hex-literal = "0.1.0"
@@ -48,6 +49,7 @@ std = [
 	"substrate-runtime-staking/std",
 	"substrate-runtime-system/std",
 	"substrate-runtime-timestamp/std",
+	"substrate-runtime-version/std",
 	"serde_derive",
 	"serde/std",
 	"log",
diff --git a/polkadot/runtime/src/lib.rs b/polkadot/runtime/src/lib.rs
index 6452aadcfd..532de07cd7 100644
--- a/polkadot/runtime/src/lib.rs
+++ b/polkadot/runtime/src/lib.rs
@@ -56,6 +56,8 @@ extern crate substrate_runtime_session as session;
 extern crate substrate_runtime_staking as staking;
 extern crate substrate_runtime_system as system;
 extern crate substrate_runtime_timestamp as timestamp;
+#[macro_use]
+extern crate substrate_runtime_version as version;
 
 #[cfg(feature = "std")]
 mod checked_block;
@@ -69,6 +71,7 @@ pub use staking::address::Address as RawAddress;
 
 use primitives::{AccountId, AccountIndex, Balance, BlockNumber, Hash, Index, Log, SessionKey, Signature};
 use runtime_primitives::{generic, traits::{HasPublicAux, BlakeTwo256, Convert}};
+use version::RuntimeVersion;
 
 #[cfg(feature = "std")]
 pub use runtime_primitives::BuildStorage;
@@ -102,6 +105,22 @@ pub type Block = generic::Block<Header, UncheckedExtrinsic>;
 #[cfg_attr(feature = "std", derive(Debug, Serialize, Deserialize))]
 pub struct Concrete;
 
+/// Polkadot runtime version.
+pub const VERSION: RuntimeVersion = RuntimeVersion {
+	spec_name: ver_str!("polkadot"),
+	impl_name: ver_str!("parity-polkadot"),
+	authoring_version: 0,
+	spec_version: 0,
+	impl_version: 0,
+};
+
+impl version::Trait for Concrete {
+	const VERSION: RuntimeVersion = VERSION;
+}
+
+/// Version module for this concrete runtime.
+pub type Version = version::Module<Concrete>;
+
 impl HasPublicAux for Concrete {
 	type PublicAux = AccountId;	// TODO: Option<AccountId>
 }
@@ -221,6 +240,7 @@ impl_outer_config! {
 
 pub mod api {
 	impl_stubs!(
+		version => |()| super::Version::version(),
 		authorities => |()| super::Consensus::authorities(),
 		initialise_block => |header| super::Executive::initialise_block(&header),
 		apply_extrinsic => |extrinsic| super::Executive::apply_extrinsic(extrinsic),
diff --git a/polkadot/runtime/wasm/Cargo.lock b/polkadot/runtime/wasm/Cargo.lock
index 82cbbb68e9..b5b23aa1d4 100644
--- a/polkadot/runtime/wasm/Cargo.lock
+++ b/polkadot/runtime/wasm/Cargo.lock
@@ -485,6 +485,7 @@ dependencies = [
  "substrate-runtime-support 0.1.0",
  "substrate-runtime-system 0.1.0",
  "substrate-runtime-timestamp 0.1.0",
+ "substrate-runtime-version 0.1.0",
 ]
 
 [[package]]
@@ -972,6 +973,17 @@ dependencies = [
  "substrate-runtime-system 0.1.0",
 ]
 
+[[package]]
+name = "substrate-runtime-version"
+version = "0.1.0"
+dependencies = [
+ "serde 1.0.64 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.64 (registry+https://github.com/rust-lang/crates.io-index)",
+ "substrate-codec 0.1.0",
+ "substrate-runtime-std 0.1.0",
+ "substrate-runtime-support 0.1.0",
+]
+
 [[package]]
 name = "substrate-state-machine"
 version = "0.1.0"
diff --git a/polkadot/runtime/wasm/Cargo.toml b/polkadot/runtime/wasm/Cargo.toml
index f5dc280e6f..3a73d89400 100644
--- a/polkadot/runtime/wasm/Cargo.toml
+++ b/polkadot/runtime/wasm/Cargo.toml
@@ -24,6 +24,7 @@ substrate-runtime-session = { path = "../../../substrate/runtime/session", defau
 substrate-runtime-staking = { path = "../../../substrate/runtime/staking", default-features = false }
 substrate-runtime-system = { path = "../../../substrate/runtime/system", default-features = false }
 substrate-runtime-timestamp = { path = "../../../substrate/runtime/timestamp", default-features = false }
+substrate-runtime-version = { path = "../../../substrate/runtime/version", default-features = false }
 
 [features]
 default = []
@@ -44,6 +45,7 @@ std = [
 	"substrate-runtime-staking/std",
 	"substrate-runtime-system/std",
 	"substrate-runtime-timestamp/std",
+	"substrate-runtime-version/std",
 ]
 
 [profile.release]
diff --git a/polkadot/runtime/wasm/genesis.wasm b/polkadot/runtime/wasm/genesis.wasm
index 07c28e8cff..c862998de6 100644
Binary files a/polkadot/runtime/wasm/genesis.wasm and b/polkadot/runtime/wasm/genesis.wasm differ
diff --git a/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.compact.wasm b/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.compact.wasm
index 5010850d88..f114ea539b 100644
Binary files a/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.compact.wasm and b/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.compact.wasm differ
diff --git a/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.wasm b/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.wasm
index 77c56b6c0a..0794dc20ff 100755
Binary files a/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.wasm and b/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.wasm differ
diff --git a/polkadot/transaction-pool/src/lib.rs b/polkadot/transaction-pool/src/lib.rs
index 1fab5d481e..5f344035ce 100644
--- a/polkadot/transaction-pool/src/lib.rs
+++ b/polkadot/transaction-pool/src/lib.rs
@@ -180,7 +180,7 @@ impl txpool::Scoring<VerifiedTransaction> for Scoring {
 
 /// Readiness evaluator for polkadot transactions.
 pub struct Ready<'a, A: 'a + PolkadotApi> {
-	at_block: A::CheckedBlockId,
+	at_block: BlockId,
 	api: &'a A,
 	known_nonces: HashMap<AccountId, ::primitives::Index>,
 }
@@ -188,7 +188,7 @@ pub struct Ready<'a, A: 'a + PolkadotApi> {
 impl<'a, A: 'a + PolkadotApi> Ready<'a, A> {
 	/// Create a new readiness evaluator at the given block. Requires that
 	/// the ID has already been checked for local corresponding and available state.
-	fn create(at: A::CheckedBlockId, api: &'a A) -> Self {
+	fn create(at: BlockId, api: &'a A) -> Self {
 		Ready {
 			at_block: at,
 			api,
@@ -244,12 +244,12 @@ impl<'a, A: 'a + PolkadotApi> txpool::Ready<VerifiedTransaction> for Ready<'a, A
 	}
 }
 
-pub struct Verifier<'a, A: 'a, B> {
+pub struct Verifier<'a, A: 'a> {
 	api: &'a A,
-	at_block: B,
+	at_block: BlockId,
 }
 
-impl<'a, A> Verifier<'a, A, A::CheckedBlockId> where
+impl<'a, A> Verifier<'a, A> where
 	A: 'a + PolkadotApi,
 {
 	const NO_ACCOUNT: &'static str = "Account not found.";
@@ -267,7 +267,7 @@ impl<'a, A> Verifier<'a, A, A::CheckedBlockId> where
 	}
 }
 
-impl<'a, A> txpool::Verifier<UncheckedExtrinsic> for Verifier<'a, A, A::CheckedBlockId> where
+impl<'a, A> txpool::Verifier<UncheckedExtrinsic> for Verifier<'a, A> where
 	A: 'a + PolkadotApi,
 {
 	type VerifiedTransaction = VerifiedTransaction;
@@ -322,7 +322,7 @@ impl<A> TransactionPool<A> where
 	pub fn import_unchecked_extrinsic(&self, block: BlockId, uxt: UncheckedExtrinsic) -> Result<Arc<VerifiedTransaction>> {
 		let verifier = Verifier {
 			api: &*self.api,
-			at_block: self.api.check_id(block)?,
+			at_block: block,
 		};
 		self.inner.submit(verifier, vec![uxt]).map(|mut v| v.swap_remove(0))
 	}
@@ -332,7 +332,7 @@ impl<A> TransactionPool<A> where
 		let to_reverify = self.inner.remove_sender(None);
 		let verifier = Verifier {
 			api: &*self.api,
-			at_block: self.api.check_id(block)?,
+			at_block: block,
 		};
 
 		self.inner.submit(verifier, to_reverify.into_iter().map(|tx| tx.original.clone()))?;
@@ -358,8 +358,7 @@ impl<A> TransactionPool<A> where
 
 	/// Cull old transactions from the queue.
 	pub fn cull(&self, block: BlockId) -> Result<usize> {
-		let id = self.api.check_id(block)?;
-		let ready = Ready::create(id, &*self.api);
+		let ready = Ready::create(block, &*self.api);
 		Ok(self.inner.cull(None, ready))
 	}
 
@@ -367,8 +366,7 @@ impl<A> TransactionPool<A> where
 	pub fn cull_and_get_pending<F, T>(&self, block: BlockId, f: F) -> Result<T> where
 		F: FnOnce(txpool::PendingIterator<VerifiedTransaction, Ready<A>, Scoring, Listener<Hash>>) -> T,
 	{
-		let id = self.api.check_id(block)?;
-		let ready = Ready::create(id, &*self.api);
+		let ready = Ready::create(block, &*self.api);
 		self.inner.cull(None, ready.clone());
 		Ok(self.inner.pending(ready, f))
 	}
@@ -413,7 +411,7 @@ mod tests {
 	use super::TransactionPool;
 	use substrate_keyring::Keyring::{self, *};
 	use codec::Slicable;
-	use polkadot_api::{PolkadotApi, BlockBuilder, CheckedBlockId, Result};
+	use polkadot_api::{PolkadotApi, BlockBuilder, Result};
 	use primitives::{AccountId, AccountIndex, Block, BlockId, Hash, Index, SessionKey, Timestamp,
 		UncheckedExtrinsic as FutureProofUncheckedExtrinsic};
 	use runtime::{RawAddress, Call, TimestampCall, BareExtrinsic, Extrinsic, UncheckedExtrinsic};
@@ -426,15 +424,9 @@ mod tests {
 		fn bake(self) -> Result<Block> { unimplemented!() }
 	}
 
-	#[derive(Clone)]
-	struct TestCheckedBlockId(pub BlockId);
-	impl CheckedBlockId for TestCheckedBlockId {
-		fn block_id(&self) -> &BlockId { &self.0 }
-	}
-
-	fn number_of(at: &TestCheckedBlockId) -> u32 {
-		match at.0 {
-			generic::BlockId::Number(n) => n as u32,
+	fn number_of(at: &BlockId) -> u32 {
+		match at {
+			generic::BlockId::Number(n) => *n as u32,
 			_ => 0,
 		}
 	}
@@ -457,26 +449,24 @@ mod tests {
 	}
 
 	impl PolkadotApi for TestPolkadotApi {
-		type CheckedBlockId = TestCheckedBlockId;
 		type BlockBuilder = TestBlockBuilder;
 
-		fn check_id(&self, id: BlockId) -> Result<TestCheckedBlockId> { Ok(TestCheckedBlockId(id)) }
-		fn session_keys(&self, _at: &TestCheckedBlockId) -> Result<Vec<SessionKey>> { unimplemented!() }
-		fn validators(&self, _at: &TestCheckedBlockId) -> Result<Vec<AccountId>> { unimplemented!() }
-		fn random_seed(&self, _at: &TestCheckedBlockId) -> Result<Hash> { unimplemented!() }
-		fn duty_roster(&self, _at: &TestCheckedBlockId) -> Result<DutyRoster> { unimplemented!() }
-		fn timestamp(&self, _at: &TestCheckedBlockId) -> Result<u64> { unimplemented!() }
-		fn evaluate_block(&self, _at: &TestCheckedBlockId, _block: Block) -> Result<bool> { unimplemented!() }
-		fn active_parachains(&self, _at: &TestCheckedBlockId) -> Result<Vec<ParaId>> { unimplemented!() }
-		fn parachain_code(&self, _at: &TestCheckedBlockId, _parachain: ParaId) -> Result<Option<Vec<u8>>> { unimplemented!() }
-		fn parachain_head(&self, _at: &TestCheckedBlockId, _parachain: ParaId) -> Result<Option<Vec<u8>>> { unimplemented!() }
-		fn build_block(&self, _at: &TestCheckedBlockId, _timestamp: Timestamp, _new_heads: Vec<CandidateReceipt>) -> Result<Self::BlockBuilder> { unimplemented!() }
-		fn inherent_extrinsics(&self, _at: &TestCheckedBlockId, _timestamp: Timestamp, _new_heads: Vec<CandidateReceipt>) -> Result<Vec<Vec<u8>>> { unimplemented!() }
+		fn session_keys(&self, _at: &BlockId) -> Result<Vec<SessionKey>> { unimplemented!() }
+		fn validators(&self, _at: &BlockId) -> Result<Vec<AccountId>> { unimplemented!() }
+		fn random_seed(&self, _at: &BlockId) -> Result<Hash> { unimplemented!() }
+		fn duty_roster(&self, _at: &BlockId) -> Result<DutyRoster> { unimplemented!() }
+		fn timestamp(&self, _at: &BlockId) -> Result<u64> { unimplemented!() }
+		fn evaluate_block(&self, _at: &BlockId, _block: Block) -> Result<bool> { unimplemented!() }
+		fn active_parachains(&self, _at: &BlockId) -> Result<Vec<ParaId>> { unimplemented!() }
+		fn parachain_code(&self, _at: &BlockId, _parachain: ParaId) -> Result<Option<Vec<u8>>> { unimplemented!() }
+		fn parachain_head(&self, _at: &BlockId, _parachain: ParaId) -> Result<Option<Vec<u8>>> { unimplemented!() }
+		fn build_block(&self, _at: &BlockId, _timestamp: Timestamp, _new_heads: Vec<CandidateReceipt>) -> Result<Self::BlockBuilder> { unimplemented!() }
+		fn inherent_extrinsics(&self, _at: &BlockId, _timestamp: Timestamp, _new_heads: Vec<CandidateReceipt>) -> Result<Vec<Vec<u8>>> { unimplemented!() }
 
-		fn index(&self, _at: &TestCheckedBlockId, _account: AccountId) -> Result<Index> {
+		fn index(&self, _at: &BlockId, _account: AccountId) -> Result<Index> {
 			Ok((_account[0] as u32) + number_of(_at))
 		}
-		fn lookup(&self, _at: &TestCheckedBlockId, _address: RawAddress<AccountId, AccountIndex>) -> Result<Option<AccountId>> {
+		fn lookup(&self, _at: &BlockId, _address: RawAddress<AccountId, AccountIndex>) -> Result<Option<AccountId>> {
 			match _address {
 				RawAddress::Id(i) => Ok(Some(i)),
 				RawAddress::Index(_) if self.no_lookup.load(atomic::Ordering::SeqCst) => Ok(None),