Banks are seeing an increase in the numbers of homeowners deciding voluntarily to hand back their properties because they cannot afford to keep up mortgage payments.

Voluntary repossessions involve the bank selling the property at auction but this will not show up in official figures as a repossession because there has been no court order.

The phenomenon is widespread in the US, where it has been nicknamed jingle mail because homeowners often post their keys to lenders if they cannot make the payments and no longer have any equity in their homes. It was also common in the UK recession of the early 1990s when homeowners were in negative equity.

Northern Rock, the nationalised bank, has seen a growing number of voluntary repossessions since the summer. The bank was one of the most aggressive mortgage lenders before it ran into difficulty last year and it is thought that a significant proportion of customers saying they can no longer afford their mortgages are those with Together products - where the customers took out an unsecured loan and a mortgage.

Another mainstream mortgage lender, which did not wish to be named, said it had seen cases of voluntary repossessions jump from 10 a month in January and February to 55 a month in September and October. Some of this increase relates to new build developments, particularly in industrial cities such as Liverpool and Manchester.

Another big bank said it had seen a rise - from a low base - in voluntary repossessions by consumers who faced financial problems. "This is consumers acting to manage their exposure to a downturn," the lender said.

Malcolm Hurlston, chairman of the Consumer Credit Counselling Service, which advises people in difficulty, said this was a growing issue. "About one in 10 of conversations with those who have bad mortgage problems usually starts with the borrower saying they are looking at handing back the keys," he said.

The Council of Mortgage Lenders, the industry body, said it had no data but there was some anecdotal evidence that voluntary repossessions were increasing.

"This is something we would expect in the current market conditions where the borrower may have lost their jobs and can't sell the property," it said. "But this isn't the end of the story - the property still has to be sold and the debt repaid. We would expect lenders to work with the borrowers to assist them if this is what they want to do."

Lenders can chase homeowners for mortgage debts for up to six years. A forced repossession will seriously damage a credit rating, making it hard for a borrower to secure credit in future.