By David Lawrenson

The sub prime mortgage crisis in the US has pushed up the cost of money for lenders, leading them to raise the risk premium on mortgage rates. So even though the UK base rate was held last week, mortgage rates are still on the rise.

Meanwhile, about half a million borrowers are coming to the end of fixed rate deals in the next 6-12 months and many of them are buy to let investors.

For quite a while now we have known that all was not quite right across the pond in the US mortgage market. Over zealous brokers and lenders had been recklessly advancing heavily discounted mortgages to people on low incomes to buy property. These loans were always more risky for the lender and are known in the market as "sub-prime".

Once the loans came to the end of their discounted period, many of the borrowers - who it is fair to say, were not among the most financially astute - couldn't meet their new higher repayments and the lenders who advanced the loans looked very shaky.