A new plague is stalking the shires. It strikes at random and the effect is deadly. Last seen during the housing crash of the late 1980s, gazundering is back. Annika Brocklehurst had never heard of it until two weeks ago. “I thought it was some sort of game my son played at school,” she says. “Now I know of its awful consequences.”

Gazundering is the practice of agreeing a price for a house and then offering less on the day of exchange. In Brocklehurst’s case, the buyers — who had agreed to pay £435,000 for her four-storey Georgian town house in Tunbridge Wells in June — said they would proceed only if she knocked £8,000 off the price.

“I was totally amazed by the phone call from the agent,” she says. Not only did her agent suggest Brocklehurst negotiate or accept the reduced offer, but she was advised by him, and the agent handling the sale of the house she had agreed to buy, that if she was unhappy at losing the £8,000 she should try to dilute the shortfall by passing it on.

“Their suggestion was that I demand an £8,000 reduction from the lovely lady who was selling us her farmhouse,” says Brocklehurst. “I would never behave like that. This whole experience has cost us thousands of pounds and made me realise you can trust no one.”

Her agent in Tunbridge Wells agrees the buyers acted wrongly. “At the end of the day, it was a ploy,” he says. “They had read over the weekend about house prices falling and got cold feet. In addition, they had been told by the surveyor there was £4,000 of work to be done on the basement. They came up with the £8,000 as a negotiating point. In hindsight, I think Mrs Brocklehurst should have negotiated.”

But Brocklehurst was in no mood to barter. “The buyers were told via the agent that I refused to be blackmailed into accepting less than the agreed price. They had plenty of time to change their minds about buying. To come back on the day of exchange with this is just cheap,” she says. “I am furious. They had welshed on the deal. I had our whole lives planned, the children had even chosen their rooms. Now all I have to look forward to is months of heartache as I watch the farmhouse we had fallen in love with being sold and we try to market our home again.” The house is now for sale with different agents.

According to Rob Stewart, branch manager at Hamptons International in Fulham, southwest London, gazundering will become more prevalent as the market dips. “There is a bit of a downturn and some people may feel the house they are looking to buy is no longer worth the price they offered,” he says.

“Gazundering tends to happen when the market is soft and especially when, as in Brocklehurst’s case, there is a long delay between agreeing the sale and exchanging contracts. To some people it will be seen as vile behaviour, but to others it is common sense in times of a weak market.”

Such behaviour is not unusual, says Nigel Coates, from Russell-Cooke Solicitors. “When prices start to come down, people think they can get away with it,” he says. “In England and Wales there is no legal recourse for the seller.” Coates says there is no legally binding document to protect against gazundering. “The problem is the buyer has to conclude surveys and arrange mortgages before they can commit to the purchase. Sadly, if a seller is emotionally attached to the transaction they may feel there is no alternative but to accept the reduced price.”

This was the case for Jill Holmes, from Surrey. She recently agreed to sell her £900,000 farmhouse to a young couple from Notting Hill Gate, London. On the day of exchange they knocked the price down by £85,000. Jill was recently divorced and had agreed to sell the house to downsize to a small cottage. “I was terrified that if I said no I would lose the cottage,” she says. “In retrospect I think I panicked, but I just didn’t know what else to do. It was either give in or change all my plans.” What makes the matter more galling is that Jill subsequently heard her buyers had telephoned her next-door neighbour and offered him anything he wanted for a couple of fields adjoining her property. “So it’s not as if they were short of cash,” she says. “They just thought they could get away with it. And they did.”

In Scotland, gazundering cannot in theory happen. Once you agree to buy a property you enter into a legally binding contract. There are some efforts to change things in the rest of Great Britain in order to prevent gazundering. One idea is to introduce sellers’ packs, which means that before a property can be marketed, the seller must have all the paperwork necessary for the sale to go ahead with minimum delay. But Nick Salmon, a fellow of the National Association of Estate Agents, says these will not solve the problem: “They will make it easy for the buyer to flit from one property to another as they are not having to commit to anything financially.

“They certainly won’t do anything to stop gazundering. And however questionable gazundering is morally, you have to remember that in a soft market the buyer takes advantage, just as the seller does when the market is good. It’s human nature.”

Nigel Coates, Russell-Cooke Solicitors, 020 8394 6508, www.russell-cooke.co.uk; Annika Brocklehurst’s house is now for sale with Denise Barnes, 01892 527 733, www.denisebarnes.co.uk