Senior police surgeons fear patients will be at risk because many doctors who are currently employed by police forces in the area are not prepared to work for the private firm, Veritas Management.
This is because the firm will not match rates for out-of-hours GP work, and police surgeons say they would be expected to cover large geographical areas if they work for Veritas.
GPs are also critical of the emphasis they believe the new system will place on nurses.
Police surgeons at seven police forces - Avon and Somerset, Gloucestershire, Dorset, Wiltshire, Dyfed Powys, Gwent and South Wales - are affected.
Swindon GP Dr Peter Crouch, principal police surgeon for Wiltshire until January 2006, said he would not work for Veritas.
'I have spoken to more than 20 police surgeons, including all those in Wiltshire. They have no appetite for working for Veritas, which speaks volumes,' he said.
Dr Crouch said he wanted to 'professionally distance himself' from the new system because it would involve newly appointed nurses and would be without most current police surgeons.
'There is a high medico-legal risk associated with introducing services when it is likely that none of the existing doctors will work in the system.'
A police surgeon in south west England, who did not wish to be named, said GPs would take on out-of-hours work instead because pay was better.
Veritas also confirmed its top rate of pay would be £600 for a 12-hour session from 7pm to 7am.
Dr Crouch said this was similar to the £550 rate for police surgeons in Swindon, but he pointed out that the firm would expect doctors to cover a wider area.
'With Veritas I would be based in Swindon, but would have to travel to the far side of Wiltshire. It's not feasible,' he said.
Julie Dowson, managing director of Veritas Management, said: 'If GPs are not available, we would use other doctors.'
She said there was no reason to benchmark pay rates against out-of-hours pay because the work was different. Ms Dowson said more than 100 doctors had applied to work in the service.
A spokeswoman for Wiltshire Constabulary said: 'Veritas won the regional contract with seven forces following a competitive tendering process based on both quality of service and cost, which will show a saving of around 50 per cent per annum in Wiltshire, and around 21 per cent across the region.'