Hey Rupert,
Welcome to the UK Community Page for QuickBooks Online.
We are currently experiencing some issues with our connections to Barclays, this is on the back of some maintenence that Barclays have been completing on their connections to 3rd party apps.
Our engineers are working to fix the connection. You can contact our Digital team on social media (@QuickBooksUK) and send us your e-mail address, we'll get you automatic updates as to when the connection is fixed.