Home sellers are being over-optimistic in raising the asking price of their property by more than 1.7% in April, says a report from the property website Rightmove.
This has led to a glut of unsold homes, says the company, whose House Price Index is the most up-to-date sample of residential asking prices in England and Wales.
According to the survey, it is the fourth consecutive month in which vendors have raised their asking prices, with the average across the country rising 6% in that time.
This left the average asking price at £235,822 across the country - £13,400 higher than at the end of last year - and £397,646 in Greater London, 2.2% higher than a year ago.
Rightmove warned that sellers' optimism was misplaced as an uptick in the number of homes on the market was not matched by the number of buyers prepared to complete a sale. This in turn led to the number of unsold properties on estate agents' books leaping at its fastest since May 2007.
With interest rate rises looming, Rightmove warned sellers that is they wanted to take advantage of the traditionally buoyant spring window in the housing market, they should adopt some "serious sales tactics".
Rightmove director Miles Shipside said: "With buyers still struggling to raise the necessary finance, the net result has been the biggest jump in unsold stock on agents' books that we have recorded in almost four years.
"With government cuts starting to bite and interest rate rises still expected in the second half of the year, those who are serious about selling in the spring should look to price more keenly."