To keep your account safe, follow these official guidelines from Santander UK :
If you suspect someone else knows your number, change it immediately through the Change security settings section in your online banking portal. santander 5 digit security number
Background: Given I am on the Santander Online Banking login page And I have successfully entered my Personal ID and Passcode To keep your account safe, follow these official
Attackers often use "spoofing" to appear as the bank’s fraud department, convincing users to divulge the code to "stop a fake transaction." The 5-digit number's role in authorizing new payees makes it the final barrier for criminals attempting to drain an account. 4. Conclusion To keep your account safe