Hello there, @sdjefferies.

Since you've already confirmed that both login and security questions are correct, let's perform additional troubleshooting steps using that information. First, let's make sure that your browser does not auto fill your credentials.

Here's how: 

1. Log back into your QuickBooks Self-Employed account.
2. Click the Reconnect button. 
3. Manually enter your bank’s log in credentials inside QuickBooks.
4. Click on Update Sign-in Info.

After updating the information, log back into your account. If you get the same error, you can use this article to verify the bank connection. The region is different, but the troubleshooting still applies for QuickBooks Self-Employed UK customers.  

Whenever you need help we're always here to support you. Take care and have a great day!