Seven local councils have decided to swap information and share experience and research on the threat to the historic centres, with their street markets that go back to mediaeval times or even earlier.
They say that recent changes in planning guidance from the Department of the Environment give no guarantee that out-of-town developments will be halted in future. Some of the towns have granted planning permissions for superstores that have not yet been built - and they are now regretting it.
Britain's big and medium-sized towns now all already have out-of-town superstores, and the big chains have moved on to smaller fry to complete their coverage. "We're concerned that they are coming to places like Cirencester," said Nigel Howells, chief executive of Cotswold district council, which has led the fight back.
The number of shoppers in the town's 910-year-old market has fallen and some long-established stallholders have quit. Five shops stand empty in Dyer Street, in the heart of the Gloucestershire town which has a population of 17,000.
"We've had to cut the stall rents once, and now the market traders are asking us to cut them again," Cirencester's town clerk, David Durbin, said. "It used to be a job to walk through the crowds on market days, but now it's far too easy." He and the district council say that the damage has been done by three superstores built on the town's dual carriageway bypass.
The Government has been worried enough to commission research from the chartered surveyors Hillier Parker into the damage done to smaller market towns. Russell Schiller, one of the consultants involved, said that unlike bigger towns, the smaller ones still had a large proportion of food retailers - butchers, bakers and so forth - who competed directly with the supermarkets. So when a superstore was built and started to pull customers away from the centre, the damage was all the greater.
Ross Davies, director of Oxford University's Institute of Retail Management, said that the towns' fears were justified. "As they near saturation point, the superstore chains are now moving in on these smaller communities ... these are genuine concerns.
"They're also going into retailing overseas, and developing smaller stores in city centres. We're also seeing them building stores close to their rivals in a way they have not done before, leading to more intensive competition."
The other councils involved in the initiative cover Hexham in Northumberland, Clitheroe in Lancashire, Great Malvern, Okehampton and Tavistock in Devon and Leominster in hereford and Worcester. Leominster traders have already launched a loyalty card to try and win customers back a Safeway store.
Cirencester will provide a crucial test case for the Government's planning guidance which was aimed at preventing out-of-town development. Recently, the district council refused planning permission for a retail development next to two of its out-of-town stores. The developers appealed and there was a public inquiry. Now a final decision is awaited from the Secretary of State for the Environment - and it will probably not come until after the election.
The supermarket chains have argued that they may be helping the smaller towns by building in or next to them. That, they stay, can stop local residents driving to larger towns nearby which already have superstores. If they stay in the area to do their major grocery shopping, they may also be inclined to do other buying there too.
Keith Vaz, Labour's planning spokesman, said: "We will support these smaller towns all the way - we are a party of the town centre."
Heritage versus the hard sell: Towns on the edge
In Hexham, Northumberland, Safeway wants planning permission to build a 9,000 sq ft supermarket on the edge of the town, and has appealed to the Department of the Environment after the council failed to make a decision.
The council and traders fear the store will pull shoppers away from the historic core because it is on the other side of a busy main road. With a 30,000 sq ft Co-op superstore having recently been built in the middle of town, they fear Hexham - which is on the edge of Newcastle's commuter belt - is being ``overshopped.''
In the Victorian spa town of Great Malvern in Worcestershire, local authorities are weighing up the damage done to the centre by a major edge-of-town development which included a Safeway superstore. Planning permission has also been granted for other out-of-town, non-food stores which have yet to be built.
Recently Tesco applied for planning permission for a large supermarket on a suburban site. And Waitrose has also applied to build a superstore twice its size in the heart of town, igniting a fierce debate.
On the one hand, it is preferable to an out-of-town building because it would draw shoppers in and boost the core's economy. On the other it would increase traffic and be bound to harm traders already there - including a smaller Somerfield store.Reuse content