The banks say the new "GetCash" service is ideal for customers who have lost or forgotten their bank card, but it can also be activated by any customer who would rather use their mobile to access their cash.

The new phone app allows customers to specify how much they want to withdraw.

A unique six-digit pin is then displayed and can be used at a cash machine. Once the amount of money is confirmed at the ATM the funds are released.

The app is available to more than a million RBS and NatWest customers in Scotland and millions more living throughout the rest of the UK.

Ben Green, head of mobile at both banks, said: "This has never been done anywhere in the UK, yet is a really simple and secure way to help our customers get cash whenever and wherever they need it.

"We've heard countless stories from customers who've left their wallet behind or parents who need a quick way to send money across to their children immediately.

"GetCash means these problems have been solved in a totally secure and painless way."

The RBS Group, which already operates an emergency cash service which has been used by almost 60,000 customers so far this year , is expected to introduce a range of other mobile services.