Great Western Ambulance Service (GWAS) could merge with the South Western Ambulance service.

If agreed, the area covered by the merged service would stretch from the Cotswolds in Gloucestershire down to the Isles of Scilly.

The South Western service, which covers Cornwall, Devon, Somerset and Dorset, is the only one to have expressed an interest in partnering GWAS, England’s smallest ambulance service.

But sceptical North Wiltshire MP James Gray has expressed concerns about the potential partnership.

At the GWAS annual meeting in Chippenham last Thursday, Mr Gray told executives he feared ambulances from Wiltshire would be sent to incidents in the south west.

He said: “I was told five years ago Wiltshire Ambulance Service was too small and merging with Gloucestershire and Avon to form GWAS would be a fantastic solution. I argued at the time that rural ambulance services would be watered out into urban areas and I have experience of this, with Malmesbury crews going to Bath.

“If we do the same again and amalgamate with the South West, we will end up with an enormous organisation and rural places like Wiltshire will be damaged.

“I am personally strongly opposed to the notion of a regional ambulance service which you are proposing. I think it will be substantially worse for my constituents. ”

Mr Gray suggested a return to an ambulance service for Wiltshire working in co-operation with the police and fire services.

Martin Flaherty, the interim chief executive of GWAS, said: “I don’t agree a bigger service means you necessarily lose the local feeling of your ambulance service. The ambulance stations in Wiltshire will still be the ambulance stations and the ambulance staff will still be the same.”

GWAS wants to partner with another organisation because, it says, on its own it would not be viable to become a Foundation Trust.

South Western Ambulance Service is a Foundation Trust and was named ambulance trust of the year in the 2011 Emergency Service Awards.

Its chief executive, Ken Wenman, said: “As an ambulance service that has already attained NHS Foundation Trust status, coupled with the fact the two services are closely linked geographically, it is logical that a partnership between the two is considered. It is, however, an expression of interest only at this stage.

“The priority of both services is to continue improving patient care across the region, as well as protecting their workforces.”

GWAS Unison branch spokesman Chris Hewett said: “We will be looking very closely at any developments and changes to make sure local communities are supported.”

A decision on any merger is likely to be made in the next month.