GPs are being paid twice to cover their commissioning workload regardless of whether or not locum support is required under the government's health reform.
Freedom of Information requests to 54 PCTs in England by the Labour Party found huge variations in the hourly rates being paid to commissioning GPs.
Rates range from £48 per hour in County Durham to £115 per hour in Hertfordshire.
The figures also show while Wiltshire GPs are paid £26,000 per year to cover their commissioning duties, CCG Chairs in Coventry are paid £35,000 each.
GPs will also be paid "additional sums" to attend commissioning board meetings regardless of whether locum cover is required, the Labour Party's investigation found.
Shadow Health Secretary Andy Burnham warned the "hidden cost" of locum cover could run into tens of thousands of pounds for each commissioning GP involved.
"The Government are putting GPs in a difficult situation with their plans. It makes no sense at all to take GPs away from patient care to become part-time accountants," said Burnham.
"Patients and taxpayers lose hands down as the NHS foots the bill twice."