The practice of gazundering, in which homebuyers slash the price they are willing to pay just before contracts are exchanged, has returned, say estate agents.

In some areas half of all sales are being hit by gazundering, according to the National Association of Estate Agents (NAEA). “We have seen a pickup in gazundering across the county and with sales of all values,” said Peter Bolton King, chief executive of the NAEA. “The government should stamp it out by introducing e-conveyancing and online transfers.”

John D Wood, the estate agent, recently sold a property in Wimbledon, southwest London, initially on the market for £3.7m, for about £500,000 less than its asking price. “The agreed price was around £3.5m, but the buyer dropped the price in the final days,” said the agent who worked on the sale.

Andrew Blagden, who manages Hamptons office in Farnham, Surrey, said it had a buyer who had been advised to cut the asking price of her home from £1.1m to £1m. “As a result, she reduced her offer on a £600,000 property down to £550,000,” Blagden said.

Some sellers believe they have no choice but to accept the lower price, fearing that they may miss out on the property they intend to buy next if they refuse. Others are so infuriated that they reject the gazunderers altogether.

“Gazundering is still a very risky tactic,” Bolton King said. “Any buyer who tries it should be aware that some sellers won’t only turn down the lower offer, but they will also simply refuse to do business with that buyer again.”

Robert Bailey, the founder of Robert Bailey Property, which specialises in selling London properties worth more than £1m, said two-bedroom flats in fashionable parts of the capital were particularly susceptible to seeing offer prices slashed at the last minute. But many owners preferred to put their lives on hold rather than risk falling prey to gazundering buyers, he said.

Halifax, Britain’s biggest mortgage lender, said last week that average property prices were 12.7% lower in August than a year ago.

Andy Hornby, chief executive of HBOS, the owner of Halifax, expects the credit crunch to last until 2010. “It will take a long time to play out,” he said.

“It’s going to take 18 months before US house prices start to rise – which is what’s required for the banks to have the confidence to start lending again.”