"The figures speak for themselves," Mr Williams added. "The reality is that the [guidelines] have been hugely successful in driving up densities and producing smaller homes and this inevitably reduces the number of substantial detached houses. And if they don't make them any more they go up in value."

But at the other end of the market, buyers on lower incomes are also being squeezed. In greater London, the average house price has more than doubled, from £128,000 to £287,000, since 1998. With more people squeezed out of the market, Gordon Brown is expected to announce new measures to help first-time buyers in next month's budget.

Guardian Unlimited © Guardian Newspapers Limited 2005