The bank is to compensate up to 300,000 customers who made a withdrawal at the ATM but walked away without the cash.

Unlike other banks which automatically re-credit consumer accounts when the machine retracts the forgotten cash, RBS and NatWest diverted the funds into its own 'reserves' account and only paid up if the customer asked for a refund.

The bank says it is checking its records over the past seven years and will repay the money, plus the interest earned on the sum, to customers who lost out.