Laurence Slavin, a partner at specialist medical accountants Ramsay Brown and Partners, said that both GMS and PMS profits had fallen in 2010/11.
A review of 635 full-time GP partners represented by the company found GMS profit per partner fell 2.8% from £128,580 in 2009/10 to £125,040 in 2010/11. PMS partners saw profits fall 8.8% from £156,694 to £142,980.
The data suggest the fall in GP profits has accelerated. The latest national GP income data from the NHS Information Centre showed that average GMS profit for England fell 1.2% to £99,200 in 2008/9.
Mr Slavin said PMS partners earn on average 14.3% more than GMS partners. But he said: 'This discrepancy is likely to diminish as PMS reviews continue and with a possible new contract in 2014.'
GPC negotiator Dr Richard Vautrey agreed. 'By the very nature of the local contract; PMS practices were always vulnerable,' he said.
Dr Vautrey said GP profits had been 'nose-diving'. 'There has been a dramatic increase in practice expenses,' he said.
Mr Slavin added: 'The pay rise for all GPs for 2011/12 was insignificant, VAT has increased by 2.5%, costs generally are increasing at a prohibitive rate, and those savings that could have been made have probably already been made.'
He said changes to prevalence weighting on QOF had also hit pay, particularly for practices in southern England.
Dr Vautrey added: 'In some areas local enhanced services have been cut and practices are finding it hard to achieve all of their QOF targets. If the team is under increased pressure, or staff have been lost, then it makes it even more difficult to maintain high QOF achievement levels.'
Mr Slavin warned: 'The future does not look promising for GPs' profits.'