Tesco has been forced to issue of flood of refunds after its efforts to go head-to-head with Asda’s price guarantee have backfired.

Tesco promised to reimburse shoppers double the amount if their shopping was found to be cheaper at Asda in a bid to stamp out Asda’s price guarantee promotion, which promises to be 10% cheaper than its rivals.

But according to the Daily Mail hundreds of customers have claimed money back after finding Tesco more expensive. It is understood several have claimed refunds of more than £100, and covered the cost of their entire basket.

Details of how to take advantage of Tesco’s refunds pledge have appeared on internet chat forums on personal finance websites and even on a Manchester United fans’ website.

Tesco has now capped the value of the refund to £20.

A Tesco spokesman said: “We were made aware via web forums that PriceCheck might not be being used for its genuine purpose by a small number of people.

“Having looked into it, we’ve taken some steps to protect the initiative.

“We have now placed a cap of £20 on any refund entitlements – the vast majority of refunds have been nowhere near this figure.

“In fact, a very small number of customers receive any refund at all after they check their real shop against Asda because they see that Tesco is cheaper.

“Separately, we have had technical issues with a comparison feature of PriceCheck which we continue to work on. In the meantime, customers can see all our prices at Tesco.com.”

An Asda spokesman told the paper: “If you claim to be the cheapest, call me old fashioned, but it helps to really be the cheapest.”