One in 10 borrowers are taking out a loan which is four times their salary or more, according to latest figures from the Liberal Democrats.
The LibDems say that during February, 10 per cent of people taking out a new homeloan borrowed between four and six times their income.
But the Council of Mortgage Lenders says one in 20 borrowers has a loan of five times income or more and one in 50 is borrowing more than seven times their income.
LibDem chief Treasury spokesman Vincent Cable says lenders and banks are fuelling the housing boom by allowing consumers to increase the amount they borrow.
The CML has moved to defend its members, saying that the majority of lenders will now take several factors other than income into consideration when assessing someone's ability to pay back a loan.