And finally…‘Please take your change…PLEASE!’

Despite flashing lights warning customers notes and coins have been dispensed into a cash tray, left cash has become so common that all of the country’s major supermarkets have put in place policies on what to do with the forgotten cash.

Two give it to charity, one hands it over to the police while another gives it back to the customer who handed it in.

Bryan Roberts, an analyst with Kantar Retail, said customers leaving cash - and cards - behind had become a major problem for supermarkets.

He said: “Even if you take a conservative estimate of £500 per store per year, and say there are 5,000 stores with self-service check-outs with cash back, that’s £2.5m already.

Sainsbury’s, Asda, Morrisons, Tesco and Waitrose all refused to say how much cash was left behind by customers every year and what happened to it.

“I don’t think it is outrageous to suggest it would run into the millions of pounds.”

Sainsbury’s, Asda, Morrisons, Tesco and Waitrose all refused to say how much cash was left behind by customers every year and what happened to it.

While The Financial Conduct Authority and the Competition and Markets Authority both said the issue does not fall within their remits, Morrisons said it follows lost property guidelines that say the money has to be handed back to whoever found it, if the owner cannot be traced.

A Morrisons spokesperson said: “Our self-service check-outs prompt customers to take their change and cash back at the end of every transaction.

“However, any forgotten money found in our self-service checkouts and handed in is kept in lost property for 13 weeks.

“If it is not claimed, after the period of 13 weeks, the customer who found and handed in the money is invited to claim the money.”

But there appears to be no hard and fast rules on what supermarkets should do with the forgotten cash.

A spokesman for Sainsbury’s said it kept money for a month and then donated to charity if it was not claimed.

Tesco said the cash was recorded as lost property and if “customers don’t collect their property after a few months it will be given to charity”.

But at Asda the cash is handed over to police after a week.

Its spokesman said: “Our colleagues record any cash found or handed to them as lost property at the customer service desk.

“The money will then be kept for a maximum of seven days and then given to the police if it isn’t collected within this timescale.”

Waitrose, meanwhile, has not made an official statement on what its standard policy is, according to the Daily Telegraph newspaper.

Miya Knights, retail technology research director at Planet Retail, said she was “surprised” there seems to be no industry-wide policy on the problem.

“I would certainly question giving it back to whoever handed it in,” she said.

“I would say most people would think a charity should benefit from other people’s misfortune.”

It is estimated there are now more than 42,000 self-scan tills in supermarkets and high street shops across Britain.