diff --git a/polkadot/Cargo.lock b/polkadot/Cargo.lock
index e86e42238c..8b8f0ce91d 100644
--- a/polkadot/Cargo.lock
+++ b/polkadot/Cargo.lock
@@ -8713,8 +8713,11 @@ dependencies = [
  "polkadot-collator",
  "polkadot-parachain",
  "polkadot-primitives",
+ "polkadot-service",
  "sc-client-api",
+ "sp-api",
  "sp-core",
+ "sp-runtime",
  "test-parachain-adder",
 ]
 
diff --git a/polkadot/collator/src/lib.rs b/polkadot/collator/src/lib.rs
index 070740bf7f..8e0cabb0eb 100644
--- a/polkadot/collator/src/lib.rs
+++ b/polkadot/collator/src/lib.rs
@@ -67,7 +67,7 @@ pub use sc_network::PeerId;
 pub use service::{RuntimeApiCollection, Client};
 pub use sc_cli::SubstrateCli;
 #[cfg(not(feature = "service-rewr"))]
-use polkadot_service::{FullNodeHandles, AbstractClient};
+use polkadot_service::{FullNodeHandles, AbstractClient, ClientHandle};
 #[cfg(feature = "service-rewr")]
 use polkadot_service_new::{
 	self as polkadot_service,
@@ -77,6 +77,7 @@ use sc_service::SpawnTaskHandle;
 use sp_core::traits::SpawnNamed;
 use sp_runtime::traits::BlakeTwo256;
 use consensus_common::SyncOracle;
+use sc_client_api::Backend as BackendT;
 
 const COLLATION_TIMEOUT: Duration = Duration::from_secs(30);
 
@@ -117,14 +118,19 @@ pub trait BuildParachainContext {
 	type ParachainContext: self::ParachainContext;
 
 	/// Build the `ParachainContext`.
-	fn build<SP>(
+	fn build<SP, Client, Backend>(
 		self,
-		client: polkadot_service::Client,
+		client: Arc<Client>,
 		spawner: SP,
 		network: impl Network + SyncOracle + Clone + 'static,
 	) -> Result<Self::ParachainContext, ()>
 		where
-			SP: SpawnNamed + Clone + Send + Sync + 'static;
+			SP: SpawnNamed + Clone + Send + Sync + 'static,
+			Backend: BackendT<Block>,
+			Backend::State: sp_api::StateBackend<BlakeTwo256>,
+			Client: polkadot_service::AbstractClient<Block, Backend> + 'static,
+			Client::Api: RuntimeApiCollection<StateBackend = Backend::State>,
+		;
 }
 
 /// Parachain context needed for collation.
@@ -194,11 +200,12 @@ pub async fn collate<P>(
 	Some(collation)
 }
 
+/// Build a collator service based on the `ClientHandle`.
 #[cfg(feature = "service-rewr")]
-fn build_collator_service<P>(
+pub fn build_collator_service<P>(
 	spawner: SpawnTaskHandle,
 	handles: FullNodeHandles,
-	client: polkadot_service::Client,
+	client: impl ClientHandle,
 	para_id: ParaId,
 	key: Arc<CollatorPair>,
 	build_parachain_context: P,
@@ -217,7 +224,6 @@ struct BuildCollationWork<P> {
 	key: Arc<CollatorPair>,
 	build_parachain_context: P,
 	spawner: SpawnTaskHandle,
-	client: polkadot_service::Client,
 }
 
 impl<P> polkadot_service::ExecuteWithClient for BuildCollationWork<P>
@@ -233,7 +239,7 @@ impl<P> polkadot_service::ExecuteWithClient for BuildCollationWork<P>
 		Backend: sc_client_api::Backend<Block>,
 		Backend::State: sp_api::StateBackend<BlakeTwo256>,
 		Api: RuntimeApiCollection<StateBackend = Backend::State>,
-		Client: AbstractClient<Block, Backend, Api = Api> + 'static
+		Client: AbstractClient<Block, Backend, Api = Api> + 'static,
 	{
 		let polkadot_network = self.handles
 			.polkadot_network
@@ -246,7 +252,7 @@ impl<P> polkadot_service::ExecuteWithClient for BuildCollationWork<P>
 			.ok_or_else(|| "Collator cannot run when validation networking has not been started")?;
 
 		let parachain_context = match self.build_parachain_context.build(
-			self.client,
+			client.clone(),
 			self.spawner.clone(),
 			polkadot_network.clone(),
 		) {
@@ -346,11 +352,12 @@ impl<P> polkadot_service::ExecuteWithClient for BuildCollationWork<P>
 	}
 }
 
+/// Build a collator service based on the `ClientHandle`.
 #[cfg(not(feature = "service-rewr"))]
-fn build_collator_service<P>(
+pub fn build_collator_service<P>(
 	spawner: SpawnTaskHandle,
 	handles: FullNodeHandles,
-	client: polkadot_service::Client,
+	client: impl ClientHandle,
 	para_id: ParaId,
 	key: Arc<CollatorPair>,
 	build_parachain_context: P,
@@ -366,7 +373,6 @@ fn build_collator_service<P>(
 		key,
 		build_parachain_context,
 		spawner,
-		client: client.clone(),
 	})
 }
 
@@ -454,12 +460,19 @@ mod tests {
 	impl BuildParachainContext for BuildDummyParachainContext {
 		type ParachainContext = DummyParachainContext;
 
-		fn build<SP>(
+		fn build<SP, Client, Backend>(
 			self,
-			_: polkadot_service::Client,
+			_: Arc<Client>,
 			_: SP,
 			_: impl Network + Clone + 'static,
-		) -> Result<Self::ParachainContext, ()> {
+		) -> Result<Self::ParachainContext, ()>
+		where
+			SP: SpawnNamed + Clone + Send + Sync + 'static,
+			Backend: BackendT<Block>,
+			Backend::State: sp_api::StateBackend<BlakeTwo256>,
+			Client: polkadot_service::AbstractClient<Block, Backend> + 'static,
+			Client::Api: RuntimeApiCollection<StateBackend = Backend::State>,
+		{
 			Ok(DummyParachainContext)
 		}
 	}
diff --git a/polkadot/node/test-service/src/lib.rs b/polkadot/node/test-service/src/lib.rs
index 03b8dd6aa6..f82c4b7ad3 100644
--- a/polkadot/node/test-service/src/lib.rs
+++ b/polkadot/node/test-service/src/lib.rs
@@ -26,7 +26,7 @@ use polkadot_primitives::v0::{
 	Block, Hash, CollatorId, Id as ParaId,
 };
 use polkadot_runtime_common::{parachains, registrar, BlockHashCount};
-use polkadot_service::{new_full, FullNodeHandles, AbstractClient};
+use polkadot_service::{new_full, FullNodeHandles, AbstractClient, ClientHandle, ExecuteWithClient};
 use polkadot_test_runtime::{RestrictFunctionality, Runtime, SignedExtra, SignedPayload, VERSION};
 use sc_chain_spec::ChainSpec;
 use sc_client_api::{execution_extensions::ExecutionStrategies, BlockchainEvents};
@@ -67,7 +67,7 @@ pub fn polkadot_test_new_full(
 ) -> Result<
 	(
 		TaskManager,
-		Arc<impl AbstractClient<Block, TFullBackend<Block>>>,
+		Arc<polkadot_service::FullClient<polkadot_test_runtime::RuntimeApi, PolkadotTestExecutor>>,
 		FullNodeHandles,
 		Arc<NetworkService<Block, Hash>>,
 		Arc<RpcHandlers>,
@@ -88,6 +88,15 @@ pub fn polkadot_test_new_full(
 	Ok((task_manager, client, handles, network, rpc_handlers))
 }
 
+/// A wrapper for the test client that implements `ClientHandle`.
+pub struct TestClient(pub Arc<polkadot_service::FullClient<polkadot_test_runtime::RuntimeApi, PolkadotTestExecutor>>);
+
+impl ClientHandle for TestClient {
+	fn execute_with<T: ExecuteWithClient>(&self, t: T) -> T::Output {
+		T::execute_with_client::<_, _, polkadot_service::FullBackend>(t, self.0.clone())
+	}
+}
+
 /// Create a Polkadot `Configuration`. By default an in-memory socket will be used, therefore you need to provide boot
 /// nodes if you want the future node to be connected to other nodes. The `storage_update_func` can be used to make
 /// adjustements to the runtime before the node starts.
diff --git a/polkadot/parachain/test-parachains/adder/collator/Cargo.toml b/polkadot/parachain/test-parachains/adder/collator/Cargo.toml
index dc686fe24e..cab8bbf98b 100644
--- a/polkadot/parachain/test-parachains/adder/collator/Cargo.toml
+++ b/polkadot/parachain/test-parachains/adder/collator/Cargo.toml
@@ -9,8 +9,11 @@ adder = { package = "test-parachain-adder", path = ".." }
 parachain = { package = "polkadot-parachain", path = "../../.." }
 collator = { package = "polkadot-collator", path = "../../../../collator" }
 primitives = { package = "polkadot-primitives", path = "../../../../primitives" }
+service = { package = "polkadot-service", path = "../../../../service" }
 sp-core = { git = "https://github.com/paritytech/substrate", branch = "master" }
 client-api = { package = "sc-client-api", git = "https://github.com/paritytech/substrate", branch = "master" }
+sp-runtime = { git = "https://github.com/paritytech/substrate", branch = "master" }
+sp-api = { git = "https://github.com/paritytech/substrate", branch = "master" }
 parking_lot = "0.10.0"
 codec = { package = "parity-scale-codec", version = "1.3.4" }
 futures = "0.3.4"
diff --git a/polkadot/parachain/test-parachains/adder/collator/src/main.rs b/polkadot/parachain/test-parachains/adder/collator/src/main.rs
index 2bddff6f86..318bc6142c 100644
--- a/polkadot/parachain/test-parachains/adder/collator/src/main.rs
+++ b/polkadot/parachain/test-parachains/adder/collator/src/main.rs
@@ -20,15 +20,17 @@ use std::collections::HashMap;
 use std::sync::Arc;
 
 use adder::{HeadData as AdderHead, BlockData as AdderBody};
-use sp_core::Pair;
+use sp_core::{traits::SpawnNamed, Pair};
 use codec::{Encode, Decode};
 use primitives::v0::{
-	Hash, DownwardMessage,
+	Block, Hash, DownwardMessage,
 	HeadData, BlockData, Id as ParaId, LocalValidationData, GlobalValidationData,
 };
 use collator::{ParachainContext, Network, BuildParachainContext, Cli, SubstrateCli};
 use parking_lot::Mutex;
 use futures::future::{Ready, ready, FutureExt};
+use sp_runtime::traits::BlakeTwo256;
+use client_api::Backend as BackendT;
 
 const GENESIS: AdderHead = AdderHead {
 	number: 0,
@@ -103,12 +105,19 @@ impl ParachainContext for AdderContext {
 impl BuildParachainContext for AdderContext {
 	type ParachainContext = Self;
 
-	fn build<SP>(
+	fn build<SP, Client, Backend>(
 		self,
-		_: collator::Client,
+		_: Arc<Client>,
 		_: SP,
 		network: impl Network + Clone + 'static,
-	) -> Result<Self::ParachainContext, ()> {
+	) -> Result<Self::ParachainContext, ()>
+	where
+		SP: SpawnNamed + Clone + Send + Sync + 'static,
+		Backend: BackendT<Block>,
+		Backend::State: sp_api::StateBackend<BlakeTwo256>,
+		Client: service::AbstractClient<Block, Backend> + 'static,
+		Client::Api: service::RuntimeApiCollection<StateBackend = Backend::State>,
+	{
 		Ok(Self { _network: Some(Arc::new(network)), ..self })
 	}
 }
diff --git a/polkadot/service/src/client.rs b/polkadot/service/src/client.rs
index e7743e8530..dad038cf96 100644
--- a/polkadot/service/src/client.rs
+++ b/polkadot/service/src/client.rs
@@ -118,6 +118,19 @@ pub trait ExecuteWithClient {
 			Client: AbstractClient<Block, Backend, Api = Api> + 'static;
 }
 
+/// A handle to a Polkadot client instance.
+///
+/// The Polkadot service supports multiple different runtimes (Westend, Polkadot itself, etc). As each runtime has a
+/// specialized client, we need to hide them behind a trait. This is this trait.
+///
+/// When wanting to work with the inner client, you need to use `execute_with`.
+///
+/// See [`ExecuteWithClient`](trait.ExecuteWithClient.html) for more information.
+pub trait ClientHandle {
+	/// Execute the given something with the client.
+	fn execute_with<T: ExecuteWithClient>(&self, t: T) -> T::Output;
+}
+
 /// A client instance of Polkadot.
 ///
 /// See [`ExecuteWithClient`] for more information.
@@ -129,9 +142,8 @@ pub enum Client {
 	Rococo(Arc<crate::FullClient<rococo_runtime::RuntimeApi, crate::RococoExecutor>>),
 }
 
-impl Client {
-	/// Execute the given something with the client.
-	pub fn execute_with<T: ExecuteWithClient>(&self, t: T) -> T::Output {
+impl ClientHandle for Client {
+	fn execute_with<T: ExecuteWithClient>(&self, t: T) -> T::Output {
 		match self {
 			Self::Polkadot(client) => {
 				T::execute_with_client::<_, _, crate::FullBackend>(t, client.clone())
diff --git a/polkadot/service/src/lib.rs b/polkadot/service/src/lib.rs
index b311117dd2..6bb78a18ce 100644
--- a/polkadot/service/src/lib.rs
+++ b/polkadot/service/src/lib.rs
@@ -109,16 +109,25 @@ impl IdentifyVariant for Box<dyn ChainSpec> {
 	}
 }
 
-type FullBackend = service::TFullBackend<Block>;
-type FullSelectChain = sc_consensus::LongestChain<FullBackend, Block>;
-type FullClient<RuntimeApi, Executor> = service::TFullClient<Block, RuntimeApi, Executor>;
-type FullGrandpaBlockImport<RuntimeApi, Executor> = grandpa::GrandpaBlockImport<
+/// Polkadot's full backend.
+pub type FullBackend = service::TFullBackend<Block>;
+
+/// Polkadot's select chain.
+pub type FullSelectChain = sc_consensus::LongestChain<FullBackend, Block>;
+
+/// Polkadot's full client.
+pub type FullClient<RuntimeApi, Executor> = service::TFullClient<Block, RuntimeApi, Executor>;
+
+/// Polkadot's full Grandpa block import.
+pub type FullGrandpaBlockImport<RuntimeApi, Executor> = grandpa::GrandpaBlockImport<
 	FullBackend, Block, FullClient<RuntimeApi, Executor>, FullSelectChain
 >;
 
-type LightBackend = service::TLightBackendWithHash<Block, sp_runtime::traits::BlakeTwo256>;
+/// Polkadot's light backend.
+pub type LightBackend = service::TLightBackendWithHash<Block, sp_runtime::traits::BlakeTwo256>;
 
-type LightClient<RuntimeApi, Executor> =
+/// Polkadot's light client.
+pub type LightClient<RuntimeApi, Executor> =
 	service::TLightClientWithBackend<Block, RuntimeApi, Executor, LightBackend>;
 
 #[cfg(feature = "full-node")]