Britain's homeowners face paying an extra £1.3 billion a year because mortgage lenders have increased their profit margins to recoup their losses from bad debts.

Figures reveal that lenders have increased their margin fourfold over the past year, and consumer groups are accusing “reckless” banks of “plundering” homeowners.

Eddy Weatherill, chief executive of the Independent Banking Advisory Service, said: “They all got into this position and now the customer is going to pay for it.”

The new figures, compiled by Deutsche Bank, analyse the margin between the rate at which a bank or building society borrows money and the fixed-rate deals it offers. In some cases the margin has increased eightfold in a year.

In 2007 a homeowner on a standard two-year fixed-rate deal with a small deposit would typically have paid an interest rate just 0.2% higher than the rate at which their financial institution borrowed the money. That mark-up has now increased to more than 1.6%.

The increase is bad news for the 1.4m homeowners who are coming to the end of their fixed-rate deals this year.

They already face a dwindling choice of mortgage products and are likely to face bigger monthly payouts, despite falling interest rates.

A year ago Halifax was so keen to attract new business that its two-year fixed-rate deal, at 5.14%, was lower than the rate at which it could borrow the money, which was 5.64%.

The cost of borrowing for lenders for fixed-rate deals, known as the “swap rate”, has now dropped to 4.89% but Halifax’s two-year deal is currently 5.99%.

Its rival lender Abbey has also increased the cost of fixed rates recently despite the fall in the cost of borrowing. Indeed these increases are reflected across the sector, with the average margin on fixed rates now 1.05%, compared with a margin of 0.255% a year ago.

The estimated cost to consumers is an extra £110m a month in payments, or £1.3 billion per year. Experts say the credit crunch has moved “pricing power” from borrowers back to lenders.

Ray Boulger, of Charcol, an online mortgage broker, said: “Lenders are writing new fixed-rate business at better margins than they have done for years.

“Where lenders have had to make big write-downs on mortgage-backed securities, they have got to replenish their balance sheets somehow, and the only way they can do that is to make bigger profit margins or issue new shares.”

A spokesman for the Council of Mortgage Lenders said the market had been “extremely competitive” but some of the deals on offer a year ago were “not sustainable in current market conditions”.