Norwich & Peterborough has moved to stop big borrowers locking in to low-rate deals in advance. Sunday Times

This has become common practice during the credit crunch as consumers borrowing later in the year seek to snap up good deals before the market deteriorates further.

The building society’s broker-only arm, Astra, said last week it would no longer honour advertised rates if funding costs became more expensive after an application was submitted.

Borrowers could end up with a higher rate at a later stage if the lender decides they are higher risk, or if wholesale market rates deteriorate.

Stewart Hunter at Astra, said: 'If the borrower’s risk profile is good and there’s no bad credit we will issue an offer – but we won’t guarantee to sign off the original rate applied for.'

He said that brokers had been 'abusing the system' by applying for low rates in advance.