The number of loans climbed 17-per cent from the second half of 2005 to 152,500 with their collective value increasing 20-per cent to £17.5bn. There are currently 767,000 residential buy-to-let mortgages in the UK totalling £83.9bn, the Council of Mortgage Lenders (CML) said.

But more borrowers also fell behind with repayments, with 0.73-per cent of buy-to-let mortgages in arrears of three months or more, up from 0.68-per cent over the previous six months.

Underwriting criteria remained unchanged with the average maximum loan-tovalue standing at 85-per cent and lenders requiring rental income to exceed mortgage repayments by at least 25-per cent.

Michael Coogan, director general of the CML, said: "The buy-to-let market remains robust but the view that interest rates are now more firmly on an upward trend is likely to cause the rapid growth of buy-to-let investment to slow."