diff --git a/application/CohortManager/src/Functions/ParticipantManagementServices/UpdateBlockedFlag/BlockParticipantHandler.cs b/application/CohortManager/src/Functions/ParticipantManagementServices/UpdateBlockedFlag/BlockParticipantHandler.cs
index 0c7646d8eb..05464039bb 100644
--- a/application/CohortManager/src/Functions/ParticipantManagementServices/UpdateBlockedFlag/BlockParticipantHandler.cs
+++ b/application/CohortManager/src/Functions/ParticipantManagementServices/UpdateBlockedFlag/BlockParticipantHandler.cs
@@ -53,8 +53,20 @@ public async Task<BlockParticipantResult> BlockParticipant(BlockParticipantDto b
             return new BlockParticipantResult(false, "Participant Already Blocked");
         }
 
+        var pdsParticipant = await GetPDSParticipant(blockParticipantRequest.NhsNumber);
+
+        if (pdsParticipant == null )
+        {
+            return new BlockParticipantResult(false, "Participant details do not match a record in PDS");
+        }
+
         var participantDemographic = await _participantDemographicDataService.GetSingleByFilter(x => x.NhsNumber == blockParticipantRequest.NhsNumber);
 
+        if (participantDemographic == null)
+        {
+            return new BlockParticipantResult(false, "Can not retrieve record from demographic");
+        }
+
         if (!ValidateRecordsMatch(participantDemographic, blockParticipantRequest))
         {
             _logger.LogWarning("Participant didn't pass three point check and cannot be blocked");
diff --git a/tests/UnitTests/ParticipantManagementServicesTests/UpdateBlockedFlagTests/UpdateBlockedFlagTests.cs b/tests/UnitTests/ParticipantManagementServicesTests/UpdateBlockedFlagTests/UpdateBlockedFlagTests.cs
index 209b8bead4..4da5f0348d 100644
--- a/tests/UnitTests/ParticipantManagementServicesTests/UpdateBlockedFlagTests/UpdateBlockedFlagTests.cs
+++ b/tests/UnitTests/ParticipantManagementServicesTests/UpdateBlockedFlagTests/UpdateBlockedFlagTests.cs
@@ -86,6 +86,18 @@ public async Task BlockParticipant_ExistingParticipant_ReturnsSuccess()
                 DateOfBirth = "19231012"
             });
 
+        var pdsDemoResponse = JsonSerializer.Serialize(
+            new PdsDemographic
+            {
+                NhsNumber = "6427635034",
+                FamilyName = "Jones",
+                DateOfBirth = "1923-10-12"
+            });
+
+        _mockHttpClient.Setup(x => x.SendGet("RetrievePdsDemographicUrl", It.IsAny<Dictionary<string, string>>()))
+            .ReturnsAsync(pdsDemoResponse);
+
+
         _mockParticipantManagementClient.Setup(x => x.Update(It.IsAny<ParticipantManagement>()))
             .ReturnsAsync(true);
         _mockHttpClient.Setup(x => x.SendPost("NemsUnsubscribeUrl", It.IsAny<Dictionary<string, string>>()))
@@ -94,13 +106,13 @@ public async Task BlockParticipant_ExistingParticipant_ReturnsSuccess()
                 StatusCode = HttpStatusCode.OK
             });
 
-
         //act
         var result = await _sut.BlockParticipant(_request.Object);
 
         //asset
         Assert.AreEqual(HttpStatusCode.OK, result.StatusCode);
         _mockHttpClient.Verify(x => x.SendPost("NemsUnsubscribeUrl", It.IsAny<Dictionary<string, string>>()), Times.Once);
+        _mockHttpClient.Verify(x => x.SendGet("RetrievePdsDemographicUrl", It.IsAny<Dictionary<string, string>>()), Times.Once);
         _mockParticipantManagementClient.Verify(x => x.Update(It.IsAny<ParticipantManagement>()), Times.Once);
         _mockHttpClient.VerifyNoOtherCalls();
     }
@@ -232,10 +244,11 @@ public async Task BlockParticipant_ExistingParticipantFailsThreePointCheck_Retur
         //asset
         Assert.AreEqual(HttpStatusCode.BadRequest, result.StatusCode);
         _mockHttpClient.Verify(x => x.SendPost("NemsUnsubscribeUrl", It.IsAny<Dictionary<string, string>>()), Times.Never);
+        _mockHttpClient.Verify(x => x.SendGet("RetrievePdsDemographicUrl", It.IsAny<Dictionary<string, string>>()), Times.Once);
         _mockHttpClient.VerifyNoOtherCalls();
         _mockParticipantManagementClient.Verify(x => x.GetSingleByFilter(It.IsAny<Expression<Func<ParticipantManagement, bool>>>()), Times.Once);
         _mockParticipantManagementClient.VerifyNoOtherCalls();
-        _mockParticipantDemographicClient.Verify(x => x.GetSingleByFilter(It.IsAny<Expression<Func<ParticipantDemographic, bool>>>()), Times.Once);
+        _mockParticipantDemographicClient.Verify(x => x.GetSingleByFilter(It.IsAny<Expression<Func<ParticipantDemographic, bool>>>()), Times.Never);
         _mockParticipantDemographicClient.VerifyNoOtherCalls();
     }
     [TestMethod]