“Garden grabbing” now accounts for 15 per cent of all new housing as family homes in towns and suburbs are pulled down by developers and replaced with flats.

The Conservatives, who obtained the figures from the Department for Communities and Local Government, said that the public was being “deceived”.

Greg Clark, Tory MP for Tunbridge Wells, said: “Most people assume that when the Government talks about building on brownfield sites it means ex-industrial land, like disused factories and railway sidings. They have no idea that much of it is actually beautiful, green, environmentally important gardens.”

Homeowners, especially those with large gardens, are frequently targeted by developers who make extravagant offers with the intention of building flats on the site.

Although neighbours usually object, local authorities are reluctant to turn down planning applications for flats because time and again they lose on appeal when the developers take the case to the department.

Because the Government has classified homes and gardens as brownfield sites, there is always a presumption that planning applications should be approved at appeal.

Mr Clark has launched a campaign to protect gardens from development. “All around the country perfectly decent family houses are being demolished by developers so that they can cram high-density housing on to garden land.

“This makes a mockery of a planning system which should be prioritising genuine brownfield sites for development,” he said.

MPs often receive letters from constituents complaining that their street has been spoilt by the construction of a block of flats. The problem is particularly acute in Surrey and Kent, where demand for new housing is extremely high.

The Government wants 60 per cent of all new housing to be built on brownfield sites. Ministers set the target to show that they were protecting the countryside as they embarked on a massive homebuilding programme.

In January they announced that the most up-to-date figures showed that 72 per cent of new housing was provided on brownfield sites.

A spokesman for the Department for Communities and Local Government defended the housing programme. “The proportion of new homes built on non-residential brownfield land such as industrial and derelict sites has increased substantially since 1997 and the proportion built on residential sites is now far lower than in 1985,” he said.

“Of course, it is the case that when old housing in our towns and cities needs replacing that developers build on residential land where the old housing stood.”

He also said that local government had enough powers to protect green areas. “Local authorities have plenty of powers to protect gardens if proposed development is inappropriate. New homes have to be built somewhere and we make no apology for prioritising suitable brownfield sites to increase the protection of the countryside.”

Mr Clark has tabled a Bill to close the loophole and MPs will get the opportunity to vote on it on July 14.

The Bill has cross-party support but will not proceed any further unless the Government grants it time.

MPs fear that even more lawns could be seized for development after a government-backed report this year suggested that any back garden of 100ft long or more was prime land for housing. ()

AN UNWELCOME DEVELOPMENT?

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