The price comparison website uSwitch.com has accused high street banks of acting irresponsibly in issuing millions of credit cards without checking customers' financial status.

It said that 4.8 million cards had been issued in the past 12 months, with less than 10 per cent of borrowers being asked for the most basic proof of income, such as a payslip.

Simeon Linstead, head of personal finance at uSwitch, said: “In a deteriorating economy, affordability checks should be the No 1 priority. Further checks could be costly for lenders and could lead to a decline in the number of accepted applications, but they would be a small price to pay if it helps to curb bad debt write-offs and personal indebtedness.”

A spokesman for the Consumer Credit Counselling Service, a debt charity, said: “The lack of basic checks is a worry. As the credit crunch takes its toll on consumers' finances, many people may be tempted to lie on credit application forms. It is vital there are rigorous checks put in place to ensure more credit is not given to borrowers who are already overstretched.”

The British Bankers' Association reacted angrily to the accusations. A spokesman said: “USwitch is again indulging in fantasy finance. These simplistic calculations fail to address the real issues facing customers in financial hardship.

“Banks seek to lend responsibly and will look carefully at people's finances before making credit available. They make checks before lending and do not need customers to provide payslips or bills to prove their income and outgoings.”

The row over lending practices came as George Osborne, the Shadow Chancellor, said that a Conservative government would clamp down on store cards. A third of the 27 most popular of these charge an annual percentage rate (APR) of 25 per cent or more - almost double the average credit card rate.

Speaking at the annual conference of Which?, the consumer campaign group, last night, Mr Osborne said: “Every four minutes the amount of personal debt in Britain increases by £1 million. With the cost of living rising, that is likely to get worse.

“We need to take steps now to deal with the current problem and make sure that we don't let Britain become hooked on debt. Government has a role in setting the boundaries and ensuring fair play.”

Mr Osborne said that he would give the Office of Fair Trading greater powers to cap store card interest rates at 25 per cent and that consumers would be given a seven-day “cooling off” period in which to change their mind after signing up to a store card.

The number of store card accounts has almost doubled to 13.4 million in the past five years but they have been criticised for being sold by untrained staff who are working on a commission basis.

An investigation in 2006 by the Competition Commission concluded that there was not enough competition in the store card market and that many APRs were too high.

Even so, providers are still able to set interest rates at 29.9 per cent or more, meaning that an outstanding balance of £1,000 would cost £299 in interest payments over 12 months.

The Finance & Leasing Association rejected Mr Osborne's proposals. Stephen Sklaroff, its director-general, said: “Last year the Competition Commission completed a thorough investigation of the store card market and did not suggest that a cooling-off period was necessary.

“FLA members' store card business represents 1.3 per cent of total unsecured consumer credit. The average store card balance is just £162 and credit limits tend to be lower than for credit cards.”

Counting the cost

£3,545

Average credit limit

69.5m

Credit cards in circulation

£61m

Missed credit card payments over the past six months

£17.3bn

Written off by banks in bad debt last year, including credit cards

Source: uSwitch.com

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