More than £400 million was wiped off the combined value of Britain's big seven quoted housebuilders today over fears of impending asset writedowns. Barratt Developments and TaylorWimpey were hit the hardest.

The share price crash leaves the combined market value of the big seven at just under £4 billion. Last year their worth stood at £18.5 billion.

Housing sector stocks have plummeted this week after a string of industry surveys which, among other things, have revealed that confidence in the sector had hit a low not seen since the housing crash in the 1990s.

Today, shares in Barratt tumbled 24 per cent to 91 1/2p, a low last suffered when Barratt nearly collapsed in the early 1990s. The share fall wiped £101 million off its market value, leaving the group, which is labouring under £1.7 billion of debt, worth just £317 million.

Concerns are mounting that Barratt will be forced to write down hundreds of millions of pounds from its land holdings over the next three weeks as it is forced to reappraise with auditors the value of its sales sites in time for its June 30 financial year-end. That in turn could force Barratt closer to breaching loan-to-value covenants on its bank borrowings.

A year ago, the shares were changing hands for nearly £11, valuing the company at £3.8 billion. Under Mark Clare, the newly installed chief executive, and Mark Pain, his finance director, Barratt had just completed a £2.2 billion cash acquisition of Wilson Bowden at the height of the housing boom .

Much of the purchase price included a value placed on goodwill for the expected profits from developing hundreds of acres of bare land. Mr Clare joined Barratt from British Gas. Until his arrival, Barratt had expanded largely through organic growth.

According to figures from Dataexplorers, the research company, 14 per cent of Barratt stock is on loan to traders who have been shorting the shares since late last year. The amount of stock on loan rose to a high of 18 per cent on March 31.

Shares in Taylor Wimpey, the largest UK housebuilder, which is closing about a third of its sales offices, tumbled 15.6 per cent today - after briefly falling by a fifth - down 12p to 65p, wiping £126 million off its market value, to £686 million.

A year ago, shortly after the all-share merger of George Wimpey and Taylor Woodrow, the shares hit a high of 455 1/2p, valuing the group at £4.8 billion.

A UBS housing report out last week saw declining housing demand "a severe problem for profits in both 2008 and 2009."

Executives at quoted companies are often forced to issue a statement to the stock exchange after a sharp fall in the share price - usually 10 per cent or more - if they feel there has been any material change in trading or financial position since they last reported.

Barratt last updated on trading three weeks ago while Taylor Wimpey updated just over a month ago. Today, neither issued any statement.

Shares in Persimmon, the most lowly geared of the big housebuilders, fell 10 per cent to a long-time low of 387 1/2p, wiping £124 million from its market value, to £1.16 billion. A year ago, at the peak of the housing market, Persimmon was valued at £4.1 billion. Persimmon said in April that it would stop building on new sites until market conditions improve.

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