People with poor credit records who are looking to get on to the property ladder are being hit with higher interest rates because of the global credit crunch.

Some specialist lenders have increased their rates by 2.5%, meaning potential homeowners who want to take out a £100,000 loan will now need to find an extra £150 a month to meet their mortgage repayments.

And other firms are tightening up their lending criteria, which will make it more difficult for people to qualify for a mortgage.

Lenders have decided to make the changes as a result of the current crisis in the US sub-prime mortgage sector.

British sub-prime specialists are now finding it increasingly difficult to attract investors to help finance their mortgage book, especially at the heavy adverse end of the market, which is focused towards those with a poor credit repayment history.

Kensington Mortgages, a pioneer of the sub-prime market in the UK, has said it will raise its rates by 0.55% this week.

Alex Hammond, spokesman for the firm, said: "The increase will mean that loans are pushed out of affordability of some customers."

And Victoria Mortgages, another sub-prime specialist, has already increased its rates by up to 2.5%.

Sub-prime mortgages are aimed at people who have had difficulty with credit in the past and are likely to be rejected by mainstream lenders.

But following the crisis in the US, caused by homebuyers defaulting on loans that some experts believe should never have been agreed in the first place, lenders have become increasingly wary.

A subsidiary of Deutsche Bank, db mortgages, announced last week that it is to withdraw the self cert option on its mortgages. In addition, first-time buyers will no longer be accepted.

Mark Bergin, director of sales and marketing at db mortgages, said: "The volatility in the global financial markets and the resulting tightening of liquidity over the past few months has impacted the marketplace.

"The changes that we are making to the products ensure we retain our presence in this market sector while taking into account the increased risk profile."

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