Customers were left unable to access their accounts after a technical outage.

The incident affected TSB’s mobile app and online banking services on Monday, with more than 1,000 users reporting issues by Monday afternoon.

A spokesman for TSB said: “We’re aware some customers are experiencing issues with our mobile banking app and internet banking.

“We’re sorry for any inconvenience and are working to resolve this as soon as possible.”

Some customers said the outage prevented them from making important payments at the start of the month.

Branch and telephone banking services were not affected.

The disruption comes just ahead of TSB’s planned £2.65 billion takeover by Santander, a deal that will create the UK’s third-largest bank by number of personal current accounts.

It also follows a recent online outage at rival bank HSBC, which similarly apologised to customers for disrupted service.