A running enthusiast has found an extreme way to raise money for charity – by rummaging in bins for old Asda and Tesco receipts and exploiting a loophole in the pair's price guarantees.

Stephen Auker, from West Yorkshire (pictured, right), inputs codes from receipts others have discarded into the supermarkets' price check websites and where that shopping basket would have been cheaper at a qualifying rival, Asda or Tesco offers a refund in the form of vouchers (see the Asda and Tesco price match MSE News stories).

The technique has been termed 'wombling' after the Wombles of Wimbledon who made good use of the "things that the everyday folk leave behind", as the song goes. Stephen has been wombling since the end of February.

Under both supermarkets' price guarantee schemes, it doesn't matter who has bought the groceries all you need to do is enter the code from a valid receipt. In fact, Asda and Tesco say what Stephen does is legal.

This contrasts with Tesco's attitude to wombling a few years ago when some customers tried to use others' receipts to top up their Clubcard balance, which Tesco deemed to be against its rules.

Price match is a hot topic at present after Tesco altered its guarantee last week after shoppers made hundreds of pounds by exploiting a different loophole that allowed them to identify items they could get money back vouchers on before buying (the Tesco price match overhaul MSE News story).

While he is paid in supermarket vouchers from wombling, Stephen donates the equivalent sum to Cancer Research, for which he has already raised £34,000 from running.

He says: "Being very thrifty, I'm always looking for ways to raise more cash for my charity.

"So I was thrilled when I thought of this one, and it only came to me by accident when I stopped to pick up some litter and it was an Asda receipt, and its new advert came into my mind. So I took it home and checked it out."

How much has he made?

Stephen says he has made over £50 in his first month of wombling, mainly via Asda.

More recently, he tried his luck at Tesco and wombling worked there. He made £4 at the first attempt but says it is harder for him to try Tesco as it is a long way from his home.

Martin Lewis, MoneySavingExpert.com creator, says: "This is a brilliant piece of extreme MoneySaving.  

"If you're willing to get your hands dirty there's cash to be made – not enough to live off – but a fun little supplement. If you do try it, say it once and say it loud: 'I'm a wombler and I'm proud!'"

An Asda spokeswoman says: "We love it when people save money. And some people are savvier than others."

A Tesco spokesman says: "It's always great to learn about new, imaginative ways our customers raise money for good causes."

How the guarantees work

The Tesco and Asda price guarantees work by inputting the code contained on your receipt into their websites. They then calculate whether your basket of shopping would have been cheaper elsewhere.

Tesco pays double the difference in vouchers if a basket of goods you buy there is cheaper at Asda. So buy a basket worth £90 that would have cost £80 at Asda and you're paid £20 in Tesco vouchers.

Asda pays the difference plus 1p if a basket there is not at least 10% cheaper than the nearest rival out of Morrisons, Sainsbury's, Tesco and Waitrose.

If the rival basket came in at £100 and you paid £95, you'll get a £5.01 voucher as if it were 10% cheaper you should have paid £90 (see the Asda and Tesco price match MSE News stories for full info on each, including exclusions).

Further Reading/ Key Links

Cut costs: Supermarket Shopping Guide, Cheap Online Shopping