Queues formed outside a cashpoint at a branch of Abbey National in Bath when it started giving out £20 notes instead of £10 notes for more than six hours earlier this week.

Now officials at the bank say they want anyone who used the machine between 6pm on 11 July and 2am on 12 July to return the extra money they were given.

The bank was only alerted to the error after a honest customer called and reported what was happening.

Wrong slot

Although Abbey National would not confirm the amount it overpaid, it is believed to run into thousands.

Company spokesman Tim Harrison said all customers who took out extra cash will be written to.

He said: "We use a security company to load our ATM machines and they put the wrong notes in the wrong slot.

"We know who all the customers are who used the machine, and we will get the money back."

Mr Harrison said the error was "entirely down" to the security company, which he would not name.

He said that nearly 100 million transaction took place at Abbey National machines every year, these incidents were "statistically rare" - occurring "once or twice a year".