A RETAIL park will "suck the life" out of Mid Devon town centres if it forms part of the multi-million pound redevelopment of junction 27.
The ambitious scheme to transform a 230-acre site east of Tiverton with an Imax cinema, designer outlet village and residential areas could create more than 3,000 jobs.
But the project will draw people away from towns in the district and will threaten their economic futures, a councillor has warned.
Cllr Michael Speirs, a member of Cullompton Town Council, said: "A retail development will not pull people in; it will pull people out of towns in Mid Devon.
"Cullompton as a high street is on the up and needs to continue going that way and it does not need that kind of competition, we get enough from Taunton and Exeter."
At a meeting of Cullompton Town Council, Cllr Speirs said a Mid Devon District Council officer "absolutely assured us junction 27 would not be a retail development because they realised it would suck the life out of Cullompton, Tiverton, Crediton and Bampton."
Cllr Linda Holloway, who represents Cullompton on the district council, said a number of people at the authority pushed to have land off the M5 motorway junction at Sampford Peverell included in its development plan, but said it is down to farmers to decide what they want to do with their land.
During the debate, Cllr Speirs said "it will kill our town centre and many others" and asked why they promised there would be no retail development.
Cllr Holloway said: "The officer is not in a position to say nobody will build retail as they do not have that power – one officer cannot make things happen or not happen."
"I will go to my notes and they said, at two meetings, 'we will not allow retail, but there will be leisure'. Certainly, we were given assurances," Cllr Speirs added.
The scheme, which would not be delivered for at least five years, is backed by global fund management group Axa and supporters say it has the potential to provide a unique destination for visitors and residents to work, eat and play.
A proposed visitor zone would be the largest element and could include a centre to promote Devon and the South West, a hotel and conference centre, a multi-screen cinema or Imax cinema, an outdoor and activity retail space with demonstration area, a plant and horticultural centre and a designer/lifestyle outlet village.
Local landowner Malcolm Dudley-Williams, speaking for the developers, said: "Junction 27 is a strategic location that has the capacity to deliver a significant economic stimulus for the local area and wider region."
One farmer who owns land which developers want to transform into a visitor zone told the Gazette he was extremely reluctant to sell his fields and was not interested in the potential millions he could make from a deal. He said developers' claims the proposals would "enhance" ancient rural landscapes are ridiculous.
The Granthams live in a cottage at the junction of the B3181 and a lane which is closed to traffic and leads to the existing motorway services. At the moment their house has fields on either side but under the proposals land to the west would become housing while fields to the right would become a managed nature reserve.
"At the moment it is a lovely spot and we feel it should stay that way," they said.
