Thousands of borrowers with fixed-rate mortgage quotes from some of Britain’s biggest lenders have been told that the figures are no longer valid after banks withdrew products in preparation for rising interest rates.

Banks including Halifax, the biggest British lender, have dumped old fixed-rate products and introduced new, more expensive loans over the past fortnight in the wake of rocketing wholesale lending rates. Mortgage brokers said that at least two thirds of potential home buyers with quotes from banks or brokers would find that their cost of borrowing would be far higher when they formally applied for their mortgage.

Rob Clifford, the chief executive of Mortgage Force, a broker, said: “Even if you’ve got a written quotation or mortgage illustration in black and white, the lender isn’t obliged to make that rate available. Thousands of people will have been quoted a fixed rate and they’ll be getting excited about their house purchase but they won’t get that rate.”

Louise Cuming, the head of mortgages at Moneysupermarket.com, said that an unprecedented flurry of rate changes at the banks had been set off on April 17, when the Bank of England announced an unexpected 3.1 per cent rise in inflation on the consumer prices index. This raised fears that the Bank would increase interest rates by as much as 0.5 per cent when it met in the second week of May. “We started to see fixed-rate mortgages disappearing overnight,” Ms Cuming said.

Alliance & Leicester, Northern Rock, the Portman Building Society, the Yorkshire Building Society, Halifax and Nationwide Building Society were among the lenders to withdraw exisiting fixed-rate products over the past two weeks.

A number, including Alliance & Leicester and the Portman, reintroduced products this week with rate rises of about 0.2 to 0.3 percentage points while others, such as the Skipton Building Society, had not replaced their products by yesterday.

Banks blamed a panic rise in wholesale interest rates for the increases that prospective mortgage customers were going to suffer. Banks agree to borrow tranches of cash in the capital markets at a fixed rate, which they then lend to customers at a slightly higher rate.

Matthew Wyles, of the Portman, said that soon before the Bank of England’s inflation announcement, banks could have borrowed on a two-year fix at about 5.65 per cent. After the announcement, the wholesale borrowing cost rose to about 5.89 per cent.

“We can’t afford to take much pain when fixed-rate costs go up,” Mr Wyles said. “We have to pass it on to customers because strong competition means that there’s no fat on the business model.”