LONDON - Up to one in three or 5.5 million mortgage holders in Britain could face serious financial difficulties as a result of the U.S. subprime crisis and the tougher lending climate it has created, a study showed.

According to a report published by consumer research group Mintel on Wednesday, people with poor credit records were not the only ones at risk. Those who are self-employed or had moved house frequently were also in the firing line.

"The focus over the last few months has very much been on subprime borrowers, but they are only the tip of the iceberg," Toby Clark, a senior finance analyst at Mintel, said in a statement.

Mintel said 9 percent of British mortgage holders were classed as sub-prime, while a further 24 percent were "non-standard" and relatively high risk because they had irregular incomes.

"In today's more conservative lending climate, the unconventional financial situation of these homeowners means that they will now face higher repayments and increased lenders' fees when remortgaging or moving house," Mintel said.

The Council of Mortgage Lenders (CML), whose members accounted for 98 percent of all UK residential mortgage lending, said Mintel's figures were too high.

In an e-mail the CML said preliminary data showed around 5 to 6 percent of all outstanding mortgages were held by people with blemished credit records, while around 16 percent of mortgage loans in the last year had been extended to the self-employed.

Mintel said demand for non-standard mortgages -- a 125 billion pound market -- was set to grow as people's financial circumstances become more complicated due to rising divorce rates and the growing popularity of self-employment, but supply was unlikely to keep up.

Nearly two fifths of the adult population, or some 18 million people, probably now qualified as non-standard consumers and that figure was set to rise to 20 million by 2012, Mintel said.

"But ironically as lenders become increasingly cautious, these non-standard mortgages will become harder to come by, leaving more adults without the finances needed to buy property," Clark said.

Based on a survey of almost 2,000 adults, Mintel said one in five who were interested in getting a mortgage in future already foresaw some problems with their applications because of their income, working status or personal circumstances.

That figure could grow in the years ahead if banks become more cautious in their lending.