diff --git a/core/src/main/kotlin/net/corda/core/flows/NotaryError.kt b/core/src/main/kotlin/net/corda/core/flows/NotaryError.kt
index 03298f1751..91a8075b6d 100644
--- a/core/src/main/kotlin/net/corda/core/flows/NotaryError.kt
+++ b/core/src/main/kotlin/net/corda/core/flows/NotaryError.kt
@@ -27,9 +27,9 @@ sealed class NotaryError {
             /** Specifies which states have already been consumed in another transaction. */
             val consumedStates: Map<StateRef, StateConsumptionDetails>
     ) : NotaryError() {
-        override fun toString() = "Conflict notarising transaction $txId. " +
-                "Input states have been used in another transactions, count: ${consumedStates.size}, " +
-                "content: ${consumedStates.asSequence().joinToString(limit = 5) { it.key.toString() + "->" + it.value }}"
+        override fun toString() = "One or more input states have already been used in other transactions. Conflicting state count: ${consumedStates.size}, consumption details:\n" +
+                "${consumedStates.asSequence().joinToString(",\n", limit = 5) { it.key.toString() + " -> " + it.value }}.\n" +
+                "To find out if any of the conflicting transactions have been generated by this node you can use the hashLookup Corda shell command."
     }
 
     /** Occurs when time specified in the [TimeWindow] command is outside the allowed tolerance. */
diff --git a/tools/shell/src/integration-test/kotlin/net/corda/tools/shell/HashLookupCommandTest.kt b/tools/shell/src/integration-test/kotlin/net/corda/tools/shell/HashLookupCommandTest.kt
new file mode 100644
index 0000000000..e679c53002
--- /dev/null
+++ b/tools/shell/src/integration-test/kotlin/net/corda/tools/shell/HashLookupCommandTest.kt
@@ -0,0 +1,96 @@
+package net.corda.tools.shell
+
+import co.paralleluniverse.fibers.Suspendable
+import com.google.common.io.Files
+import com.jcraft.jsch.ChannelExec
+import com.jcraft.jsch.JSch
+import com.jcraft.jsch.Session
+import net.corda.core.crypto.SecureHash
+import net.corda.core.crypto.sha256
+import net.corda.core.flows.FlowLogic
+import net.corda.core.flows.StartableByRPC
+import net.corda.core.identity.Party
+import net.corda.core.messaging.startFlow
+import net.corda.core.utilities.getOrThrow
+import net.corda.node.services.Permissions
+import net.corda.testing.contracts.DummyContract
+import net.corda.testing.core.ALICE_NAME
+import net.corda.testing.driver.DriverParameters
+import net.corda.testing.driver.NodeHandle
+import net.corda.testing.driver.driver
+import net.corda.testing.node.User
+import org.bouncycastle.util.io.Streams
+import org.junit.Ignore
+import org.junit.Test
+import kotlin.test.assertTrue
+
+class HashLookupCommandTest {
+    @Ignore
+    @Test
+    fun `hash lookup command returns correct response`() {
+        val user = User("u", "p", setOf(Permissions.all()))
+
+        driver(DriverParameters(notarySpecs = emptyList(), extraCordappPackagesToScan = listOf("net.corda.testing.contracts"))) {
+            val nodeFuture = startNode(providedName = ALICE_NAME, rpcUsers = listOf(user), startInSameProcess = true)
+            val node = nodeFuture.getOrThrow()
+            val txId = issueTransaction(node)
+
+            val session = connectToShell(user, node)
+
+            testCommand(session, command = "hashLookup ${txId.sha256()}", expected = "Found a matching transaction with Id: $txId")
+            testCommand(session, command = "hashLookup ${SecureHash.randomSHA256()}", expected = "No matching transaction found")
+
+            session.disconnect()
+        }
+    }
+
+    private fun testCommand(session: Session, command: String, expected: String) {
+        val channel = session.openChannel("exec") as ChannelExec
+        channel.setCommand(command)
+        channel.connect(5000)
+
+        assertTrue(channel.isConnected)
+
+        val response = String(Streams.readAll(channel.inputStream))
+        val matchFound = response.lines().any { line ->
+            line.contains(expected)
+        }
+        channel.disconnect()
+        assertTrue(matchFound)
+    }
+
+    private fun connectToShell(user: User, node: NodeHandle): Session {
+        val conf = ShellConfiguration(commandsDirectory = Files.createTempDir().toPath(),
+                user = user.username, password = user.password,
+                hostAndPort = node.rpcAddress,
+                sshdPort = 2224)
+
+        InteractiveShell.startShell(conf)
+        InteractiveShell.nodeInfo()
+
+        val session = JSch().getSession("u", "localhost", 2224)
+        session.setConfig("StrictHostKeyChecking", "no")
+        session.setPassword("p")
+        session.connect()
+
+        assertTrue(session.isConnected)
+        return session
+    }
+
+    private fun issueTransaction(node: NodeHandle): SecureHash {
+        return node.rpc.startFlow(::DummyIssue).returnValue.get()
+    }
+
+    @StartableByRPC
+    internal class DummyIssue : FlowLogic<SecureHash>() {
+        @Suspendable
+        override fun call(): SecureHash {
+            val me = serviceHub.myInfo.legalIdentities.first().ref(0)
+            val fakeNotary = me.party
+            val builder = DummyContract.generateInitial(1, fakeNotary as Party, me)
+            val stx = serviceHub.signInitialTransaction(builder)
+            serviceHub.recordTransactions(stx)
+            return stx.id
+        }
+    }
+}
\ No newline at end of file
diff --git a/tools/shell/src/main/java/net/corda/tools/shell/HashLookupShellCommand.java b/tools/shell/src/main/java/net/corda/tools/shell/HashLookupShellCommand.java
new file mode 100644
index 0000000000..038e60ce0d
--- /dev/null
+++ b/tools/shell/src/main/java/net/corda/tools/shell/HashLookupShellCommand.java
@@ -0,0 +1,59 @@
+package net.corda.tools.shell;
+
+import net.corda.core.crypto.SecureHash;
+import net.corda.core.messaging.CordaRPCOps;
+import net.corda.core.messaging.StateMachineTransactionMapping;
+import org.crsh.cli.Argument;
+import org.crsh.cli.Command;
+import org.crsh.cli.Man;
+import org.crsh.cli.Usage;
+import org.crsh.text.Color;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.List;
+import java.util.Optional;
+
+public class HashLookupShellCommand extends InteractiveShellCommand {
+    private static Logger logger = LoggerFactory.getLogger(HashLookupShellCommand.class);
+
+    @Command
+    @Man("Checks if a transaction matching a specified Id hash value is recorded on this node.\n\n" +
+            "This is mainly intended to be used for troubleshooting notarisation issues when a\n" +
+            "state is claimed to be already consumed by another transaction.\n\n" +
+            "Example usage: hash-lookup E470FD8A6350A74217B0A99EA5FB71F091C84C64AD0DE0E72ECC10421D03AAC9"
+    )
+    public void main(@Usage("A hexadecimal SHA-256 hash value representing the hashed transaction Id") @Argument(unquote = false) String txIdHash) {
+        logger.info("Executing command \"hash-lookup\".");
+
+        if (txIdHash == null) {
+            out.println("Please provide a hexadecimal transaction Id hash value, see 'man hash-lookup'", Color.red);
+            return;
+        }
+
+        CordaRPCOps proxy = ops();
+        List<StateMachineTransactionMapping> mapping = proxy.stateMachineRecordedTransactionMappingSnapshot();
+
+        SecureHash txIdHashParsed;
+        try {
+            txIdHashParsed = SecureHash.parse(txIdHash);
+        } catch (IllegalArgumentException e) {
+            out.println("The provided string is not a valid hexadecimal SHA-256 hash value", Color.red);
+            return;
+        }
+
+        Optional<SecureHash> match = mapping.stream()
+                .map(StateMachineTransactionMapping::getTransactionId)
+                .filter(
+                        txId -> SecureHash.sha256(txId.getBytes()).equals(txIdHashParsed)
+                )
+                .findFirst();
+
+        if (match.isPresent()) {
+            SecureHash found = match.get();
+            out.println("Found a matching transaction with Id: " + found.toString());
+        } else {
+            out.println("No matching transaction found", Color.red);
+        }
+    }
+}
diff --git a/tools/shell/src/main/kotlin/net/corda/tools/shell/InteractiveShell.kt b/tools/shell/src/main/kotlin/net/corda/tools/shell/InteractiveShell.kt
index 21814df176..fc90960866 100644
--- a/tools/shell/src/main/kotlin/net/corda/tools/shell/InteractiveShell.kt
+++ b/tools/shell/src/main/kotlin/net/corda/tools/shell/InteractiveShell.kt
@@ -132,6 +132,7 @@ object InteractiveShell {
         ExternalResolver.INSTANCE.addCommand("run", "Runs a method from the CordaRPCOps interface on the node.", RunShellCommand::class.java)
         ExternalResolver.INSTANCE.addCommand("flow", "Commands to work with flows. Flows are how you can change the ledger.", FlowShellCommand::class.java)
         ExternalResolver.INSTANCE.addCommand("start", "An alias for 'flow start'", StartShellCommand::class.java)
+        ExternalResolver.INSTANCE.addCommand("hashLookup", "Checks if a transaction with matching Id hash exists.", HashLookupShellCommand::class.java)
         shell = ShellLifecycle(configuration.commandsDirectory).start(config, configuration.user, configuration.password)
     }