diff --git a/app/src/pages/patientSearchPage/PatientSearchPage.test.tsx b/app/src/pages/patientSearchPage/PatientSearchPage.test.tsx
index ad598ac1f..ab0cc84ba 100644
--- a/app/src/pages/patientSearchPage/PatientSearchPage.test.tsx
+++ b/app/src/pages/patientSearchPage/PatientSearchPage.test.tsx
@@ -348,6 +348,18 @@ describe('PatientSearchPage', () => {
                 });
             },
         );
+
+        it('a defined width class is applied to the NHS number input field', async () => {
+
+            const definedWidthClass = 'nhsuk-input--width-10';
+
+            renderPatientSearchPage();
+
+            const input = screen.getByTestId('nhs-number-input');
+            expect(input).toHaveClass(definedWidthClass);
+
+        });
+
     });
 });
 
diff --git a/app/src/pages/patientSearchPage/PatientSearchPage.tsx b/app/src/pages/patientSearchPage/PatientSearchPage.tsx
index 0f2b6f426..14713e548 100644
--- a/app/src/pages/patientSearchPage/PatientSearchPage.tsx
+++ b/app/src/pages/patientSearchPage/PatientSearchPage.tsx
@@ -115,6 +115,7 @@ function PatientSearchPage() {
                     <Input
                         id="nhs-number-input"
                         data-testid="nhs-number-input"
+                        className="nhsuk-input--width-10"
                         label="Enter NHS number"
                         hint="A 10-digit number, for example, 485 777 3456"
                         type="text"