diff --git a/DigitalLearningSolutions.Web.Tests/Controllers/Register/RegisterDelegateByCentreControllerTests.cs b/DigitalLearningSolutions.Web.Tests/Controllers/Register/RegisterDelegateByCentreControllerTests.cs
index 0040c2b514..0d4a77fc61 100644
--- a/DigitalLearningSolutions.Web.Tests/Controllers/Register/RegisterDelegateByCentreControllerTests.cs
+++ b/DigitalLearningSolutions.Web.Tests/Controllers/Register/RegisterDelegateByCentreControllerTests.cs
@@ -176,7 +176,7 @@ public void LearnerInformationPost_updates_tempdata_correctly()
             const string answer4 = "answer4";
             const string answer5 = "answer5";
             const string answer6 = "answer6";
-            const string professionalRegistrationNumber = "PR123456";
+            const string professionalRegistrationNumber = "PRN1234";
             var model = new LearnerInformationViewModel
             {
                 JobGroup = jobGroupId,
diff --git a/DigitalLearningSolutions.Web.Tests/Controllers/TrackingSystem/Delegates/EditDelegateControllerTests.cs b/DigitalLearningSolutions.Web.Tests/Controllers/TrackingSystem/Delegates/EditDelegateControllerTests.cs
index c08f3dbe35..5c5df8ac44 100644
--- a/DigitalLearningSolutions.Web.Tests/Controllers/TrackingSystem/Delegates/EditDelegateControllerTests.cs
+++ b/DigitalLearningSolutions.Web.Tests/Controllers/TrackingSystem/Delegates/EditDelegateControllerTests.cs
@@ -175,7 +175,7 @@ public void Index_post_returns_view_with_model_error_with_invalid_prn()
                 result.As<ViewResult>().Model.Should().BeOfType<EditDelegateViewModel>();
                 AssertModelStateErrorIsExpected(
                     result,
-                   ErrorMessagesTestHelper.InvalidFormatError
+                    "Invalid professional registration number format - Only alphanumeric characters (a-z, A-Z and 0-9) and hyphens (-) allowed"
                 );
                 A.CallTo(() => userService.GetDelegateById(A<int>._)).MustNotHaveHappened();
             }
diff --git a/DigitalLearningSolutions.Web.Tests/Helpers/ProfessionalRegistrationNumberHelperTests.cs b/DigitalLearningSolutions.Web.Tests/Helpers/ProfessionalRegistrationNumberHelperTests.cs
index a7270f280d..d78c74f042 100644
--- a/DigitalLearningSolutions.Web.Tests/Helpers/ProfessionalRegistrationNumberHelperTests.cs
+++ b/DigitalLearningSolutions.Web.Tests/Helpers/ProfessionalRegistrationNumberHelperTests.cs
@@ -1,12 +1,11 @@
 namespace DigitalLearningSolutions.Web.Tests.Helpers
 {
+    using System.Linq;
     using DigitalLearningSolutions.Web.Helpers;
-    using DigitalLearningSolutions.Web.Tests.TestHelpers;
     using FluentAssertions;
     using FluentAssertions.Execution;
     using Microsoft.AspNetCore.Mvc.ModelBinding;
     using NUnit.Framework;
-    using System.Linq;
 
     public class ProfessionalRegistrationNumberHelperTests
     {
@@ -71,7 +70,7 @@ public void ValidateProfessionalRegistrationNumber_does_not_set_errors_when_vali
         {
             // Given
             var state = new ModelStateDictionary();
-            const string validPrn = "AB123456";
+            const string validPrn = "abc-123";
 
             // When
             ProfessionalRegistrationNumberHelper.ValidateProfessionalRegistrationNumber(
@@ -105,13 +104,22 @@ public void ValidateProfessionalRegistrationNumber_sets_error_when_hasPrn_is_not
             }
         }
 
-        [TestCase(null, ErrorMessagesTestHelper.MissingNumberError)]
-        [TestCase("", ErrorMessagesTestHelper.MissingNumberError)]
-        [TestCase("1234", ErrorMessagesTestHelper.LengthError)]
-        [TestCase("1234", ErrorMessagesTestHelper.LengthError)]
-        [TestCase("01234_", ErrorMessagesTestHelper.InvalidFormatError)]
-        [TestCase("01234 ", ErrorMessagesTestHelper.InvalidFormatError)]
-        [TestCase("01234$", ErrorMessagesTestHelper.InvalidFormatError)]
+        [TestCase(null, "Enter a professional registration number")]
+        [TestCase("", "Enter a professional registration number")]
+        [TestCase("123", "Professional registration number must be between 5 and 20 characters")]
+        [TestCase("0123456789-0123456789", "Professional registration number must be between 5 and 20 characters")]
+        [TestCase(
+            "01234_",
+            "Invalid professional registration number format - Only alphanumeric characters (a-z, A-Z and 0-9) and hyphens (-) allowed"
+        )]
+        [TestCase(
+            "01234 ",
+            "Invalid professional registration number format - Only alphanumeric characters (a-z, A-Z and 0-9) and hyphens (-) allowed"
+        )]
+        [TestCase(
+            "01234$",
+            "Invalid professional registration number format - Only alphanumeric characters (a-z, A-Z and 0-9) and hyphens (-) allowed"
+        )]
         public void ValidateProfessionalRegistrationNumber_sets_error_when_prn_is_invalid(
             string prn,
             string expectedError
diff --git a/DigitalLearningSolutions.Web.Tests/TestHelpers/ErrorMessagesTestHelper.cs b/DigitalLearningSolutions.Web.Tests/TestHelpers/ErrorMessagesTestHelper.cs
deleted file mode 100644
index 7636944e7a..0000000000
--- a/DigitalLearningSolutions.Web.Tests/TestHelpers/ErrorMessagesTestHelper.cs
+++ /dev/null
@@ -1,17 +0,0 @@
-
-namespace DigitalLearningSolutions.Web.Tests.TestHelpers
-{
-    public static class ErrorMessagesTestHelper
-    {
-        public const string InvalidFormatError =
-           "Invalid professional registration number format. " +
-           "Valid formats include: 7 digits (e.g., 1234567), 1–2 letters followed by 6 digits (e.g., AB123456), " +
-           "4–8 digits, an optional 'P' plus 5–6 digits, 'C' or 'P' plus 6 digits, " +
-           "an optional letter plus 5–6 digits, 'L' plus 4–6 digits, " +
-           "or 2 digits followed by a hyphen and 4–5 alphanumeric characters (e.g., 12-AB123).";
-
-        public const string MissingNumberError = "Enter a professional registration number";
-        public const string LengthError = "Professional registration number must be between 5 and 20 characters";
-
-    }
-}
diff --git a/DigitalLearningSolutions.Web/Helpers/ProfessionalRegistrationNumberHelper.cs b/DigitalLearningSolutions.Web/Helpers/ProfessionalRegistrationNumberHelper.cs
index 130c8d52b6..461d7ae46b 100644
--- a/DigitalLearningSolutions.Web/Helpers/ProfessionalRegistrationNumberHelper.cs
+++ b/DigitalLearningSolutions.Web/Helpers/ProfessionalRegistrationNumberHelper.cs
@@ -1,7 +1,7 @@
 namespace DigitalLearningSolutions.Web.Helpers
 {
-    using Microsoft.AspNetCore.Mvc.ModelBinding;
     using System.Text.RegularExpressions;
+    using Microsoft.AspNetCore.Mvc.ModelBinding;
 
     public class ProfessionalRegistrationNumberHelper
     {
@@ -48,17 +48,13 @@ public static void ValidateProfessionalRegistrationNumber(
                 );
             }
 
-           const string pattern = @"^(\d{7}|[A-Za-z]{1,2}\d{6}|\d{4,8}|P?\d{5,6}|[C|P]\d{6}|[A-Za-z]?\d{5,6}|L\d{4,6}|\d{2}-[A-Za-z\d]{4,5})$";
+            const string pattern = @"^[a-z\d-]+$";
             var rg = new Regex(pattern, RegexOptions.IgnoreCase);
             if (!rg.Match(prn).Success)
             {
                 modelState.AddModelError(
                     "ProfessionalRegistrationNumber",
-                   "Invalid professional registration number format. " +
-        "Valid formats include: 7 digits (e.g., 1234567), 1–2 letters followed by 6 digits (e.g., AB123456), " +
-        "4–8 digits, an optional 'P' plus 5–6 digits, 'C' or 'P' plus 6 digits, " +
-        "an optional letter plus 5–6 digits, 'L' plus 4–6 digits, " +
-        "or 2 digits followed by a hyphen and 4–5 alphanumeric characters (e.g., 12-AB123)."
+                    "Invalid professional registration number format - Only alphanumeric characters (a-z, A-Z and 0-9) and hyphens (-) allowed"
                 );
             }
         }