Nick Collins, an independent London real estate broker who's had record profits every year since 2003, took a hit in September -- and that may be bad news for a U.K. economy built on a housing bubble. Five of his 50 buyers pulled out of purchases, spooked by a run on mortgage lender Northern Rock Plc that left it 2 billion pounds ($4.1 billion) poorer.

``It's undermined people's confidence,'' says Collins, 38, who sells homes worth as much as 5 million pounds. ``The market's not as frothy and competitive as it was.''

Northern Rock, which cratered after investors balked at buying its debt, is one of several signs that the U.K.'s property boom may be ending. The average home almost tripled in value in the past decade, helping fuel the country's 15-year economic expansion -- the longest in two centuries -- and buoying the governments of Tony Blair and Gordon Brown.

Now, with mortgage lending cooling and house prices falling for the first time this year in September, the economy may be in the early stages of a slowdown.

``U.K. house prices are significantly overvalued and extremely vulnerable to a correction,'' said Danny Gabay, a former Bank of England economist and a director of London-based Fathom Financial Consulting Ltd. ``The downside risks to economic growth over the next 12 months are significant.''