The buy-to-let market could be a "source of weakness" for property prices in the coming months, according to Gordon Brown's top expert on the housing market.

Kate Barker, a member of the Bank of England's Monetary Policy Committee (MPC) and the author of two Government reports on the UK planning system, said that because 12 per cent of mortgage lending now goes on buy-to-let (BTL) , "a decline in this demand, even if existing BTL owners do not decide to sell, could well dampen the market".

However, she said that financial market turbulence was unlikely to trigger a change, because a major economic slowdown was not expected, and said that a significant slowdown in the market was "not my central expectation".

She said "The evidence from business surveys and housing market indicators will be an important part of my judgement over the next few months about how far the downside risks to the outlook have increased."

Ms Barker is seen as a swing voter on the MPC and this speech will be carefully scrutinised for clues as to the future path of interest rates.

The pound firmed against other currencies in an initial reaction to her remarks.

Ms Barker said today that the housing market was "vulnerable to a major change in expectations" and appeared to be slowing.

She added that the process could be exacerbated by a decline in buy-to-let activity that may suffer from higher interest rates, little change in rents and possibly reduced expectations of price rises.

Ms Barker said in a speech to the Institute of Chartered Accountants in England and Wales that first-time buyers could enter the BTL market and support prices but they might also stay out of the sector if they expected a fall in prices.

While low rates, a stable economy and supply constraints had kept house prices growth strong, Ms Barker said that the current level of prices was "on many estimates, above a level explained by these fundamentals".

It was "therefore somewhat vulnerable to a major change in expectations about future prices".

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