A survey of 90% of the market by Rightmove, a real estate price tracking company, shows that real estate prices fell 2.9% in August, the second consecutive down month this summer.

Prices fell nearly 6% in the overheated London market.

That news dovetails ominously with the rumors of "panic selling" in London as owners try to cash in on their overpriced houses at the very top of the market.

While prices generally cool off in summer when fewer people feel like moving, according to Rightmove, the decline was the worst the agency has ever seen:

... this is the largest decrease ever recorded by Rightmove at this time of year, and a lead indicator of a slower market in the second half of 2014.