Buyers of new homes should not be too alarmed if the building society valuer slaps a much lower figure on their home than they expected, because many others are in the same boat.

Leading trade journal Building magazine says the price of new homes is being driven down by a record number of legal threats to surveyors over house valuations given before the credit crunch.

The report says 25 surveyors have been taken to court over valuations by mortgage lenders, including Barclays, compared with just one in the previous five years.

Thousands of other surveyors face legal action by no-win, no-fee lawyers, which have driven up the cost of their professional indemnity insurance and threatened to put many surveyors out of business altogether.

Roger Humber, strategic policy adviser for the House Builders Association, says: "With all this pressure, they have no other choice than to take a very cautious view.

"Small builders are having to fight every down-valuation like hell."

Since Nationwide Building Society told valuers to value brand new property at resale prices, there have been fears the "new-build premium" on brand new homes could vanish altogether.

However, despite these valuation problems, builders seem to be sharply stepping up their production levels.

Latest quarterly figures from the National House-Building Council (NHBC) says registrations for starts in March 2010 were 85 per cent up - at just over 11,000 - on March 2009 (5,954).

Notable growth in the number of starts in the January-March quarter were recorded in London (up 138 per cent to 3,100).

Overall, the NHBC says the pick-up is much larger in the private sector (by 114 per cent) than in the public sector (up 26 per cent to 9,562), which is likely to be more affected by imminent and widespread government spending cuts.