British borrowers with sub-prime mortgages may run into difficulties soon, according to one mortgage broker.

Ray Boulger, of broker firm John Charcol, told BBC Radio 4’s PM programme that people with poor credit have two distinct problems.

He identified the first as the fact that rates for initial mortgages have risen sharply recently, going as high as nine per cent in some cases.

Second, there are people that are coming to the end of their initial periods and finding that they cannot remortgage, he revealed.

This is because lending criteria have tightened recently in the face of the worldwide credit crisis, Mr Boulger explains.

People in this situation "may have no option but to go onto the revert-to rate from their original lender, which in many cases will take them well into double figures", he added.

A recent GE Money survey found that 22 per cent of mortgage brokers claim the current credit uncertainty is having an adverse effect on their business.