Banks and building societies are cashing in on the credit crunch and raising profit margins on mortgages by £1.2 billion in a year, figures show.

Wholesale funding costs last month returned to the pre-credit crunch levels. However, those taking out mortgages last month are paying £74 more a month on the average tracker and an extra £62 on fixes.

The rise in borrowing costs hits the 1.3m homeowners coming off fixed rates hardest: they are seeing repayments jump by up to £3,000 a year.

Melanie Bien of broker Savills Private Finance said: “Lenders are using the credit crunch to chase better margins.” The rate banks pay when borrowing on the wholesale market to fund fixed-rate mortgages — “swap” rates — averaged 6.22% last month, the same level as in June last year.

Then lenders were making a loss on two-year fixes, but now charge an average margin of 0.78 percentage points above swaps and 0.83 points above Libor (the rate paid by lenders funding trackers).

With about 1.3m fixes and trackers sold in the past year the cost to consumers is £1.2 billion. First-time buyers are among those hardest hit by the lenders’ strategy. Even though lenders such as Halifax, Abbey, and Yorkshire Bank slashed rates last week by up to 0.50%, those with deposits of more than 25% saw the biggest cuts.

The best two-year fix for borrowers with a 25% deposit is offered by Newcastle building society at 5.95%, which has a £1,598 fee. A borrower with an average home loan of £200,000 would pay £1,282 a month.

However, the best two-year fix for those with only a 5% deposit — Direct Line at 6.89%, which has a £499 fee and a 1.5% higher lending charge — would cost £117 a month more.