With their picture postcard cottages and cobbled streets, Sussex's market towns are held to be the epitome of rural Englishness.

But they are under threat from a creeping blight of blandness, according to a wide-ranging survey.

A report published by the Campaign to Protect Rural England (CPRE) says towns such as Lewes, Horsham and Midhurst are losing their unique character to "identikit" housing, out-of-town shopping and traffic congestion.

They are in danger of becoming little more than dormitories, with residents working in London and doing little to keep the local economy alive.

The CPRE surveyed four Sussex market towns and the cathedral city of Chichester as part of a survey of 120 locations between March and October last year.

All were deemed to be significantly threatened by increasing traffic and all but Midhurst were found to have struggling local food industries on the verge of extinction.

Developers in most were likely to build in a way which made no reference to the character of the town.

One of the most threatened market towns in Sussex, according to the report, is Lewes, where a large part of the town centre encompassing Lewes House Garden and the old Baxters printing works is about to be turned into homes.

Robert Cheeseman, chairman of the Friends of Lewes civic society, welcomed the report.

He said the biggest threat to life in Lewes was increased traffic.

He added: "We are to some extent fortunate in being constrained by the topography.

"We have the Downs on one hand and the river and flood plains on the other.

"On both, new development is not likely, particularly if we get the national park."

Tom Oliver, the CPRE's head of rural policy, said: "Towns are threatened by bland and uniform new development with nothing local about it.

"Some have been hit by retail and superstore developments out of town, which have sucked the life from their High Streets.

"The erosion of character and attractiveness matters."

Chancellor Gordon Brown has revealed plans to relax the ban on out-of-town developments, pressured by retailers including Tesco, Ikea, Asda and B&Q.

A Treasury report last week proposed the building of 1.4 million homes in England in the next ten years.

The CPRE is now lobbying the Government to impose stringent policy guidelines to save England's market towns from decline.

Mr Oliver said: "It requires constant vigilance. Every planning policy must be scrutinised.

"This is part of everyone's future and we cannot afford to let things drift."