Practices in some primary care organisations (PCOs) will share up to £1.9 million in extra prevalence funding over the next two years, a GP investigation shows.
But in other areas, similar amounts will be stripped from practices, and GP leaders say there is no guarantee it will be reinvested in primary care.
In addition, in some areas where practices stand to gain from prevalence, they could lose other work as PCOs make cuts to compensate.
Despite the scale of the funding shifts, PCOs are largely unprepared. Sixty per cent of 75 PCTs in England contacted by GP have not assessed the impact of prevalence changes. Assessments have been carried out in most of Scotland and Northern Ireland, but not in Wales.
Gains and losses are inevitable at PCO level because no money is moving between them to pay for the removal of mechanisms that currently 'damp' prevalence weighting on quality pay.
Several PCOs told GP that where GPs make large gains from prevalence, cuts could be made to balance budgets, possibly from enhanced services.
In areas of low disease, practices will lose tens of thousands of pounds, and PCOs will gain millions. Some trusts plan to reinvest the cash, others do not.
Modelling by Wiltshire GP Dr Gavin Jamie, a quality framework statistics expert, shows that the greatest prevalence gains for GPs are in Lincolnshire PCT, which will pay out an extra £1.89 million over the next two years. Seven other PCTs will see prevalence payments rise by more than £1 million.
Dr Michelle Drage, joint chief executive of Londonwide LMCs, said London GPs would lose £11 million.
'Where PCTs have gained this money there is no guarantee it will be reinvested in primary care. If PCTs are losing money, how will they afford it? It should be a transitional scheme at least.'
GPC chairman Dr Laurence Buckman said PCOs should not be exposed to swings in funding in this way. But he said practices that gain would be angry if they had to wait for extra funding.
Dr David Jenner, GMS lead at the NHS Alliance, called for PCT allocations to be linked to the prevalence formula, and for changes to be gradual.
'It's sucking money away from GPs in inner cities to those in more affluent, rural areas, where there are lots of elderly people. For some financially challenged PCTs, like mine in Devon, it could cause real problems.'
Impact of Prevalence Changes
Biggest practice losers
£200,000 - Two university practices in Leeds and Nottingham are set to lose this amount
Biggest practice winner
The proportion of PCTs that have yet to assess the impact of prevalence changes
How PCT funding for prevalence will change by 2010/11
Areas where GPs gain most
1. Lincolnshire PCT +£1,890,766
2. County Durham PCT +£1,500,083
3. Cumbria PCT +£1,242,497
4. Derbyshire County PCT +£1,228,091
5. North Lancashire PCT +£1,185,083
Areas where GPs lose most
1. Surrey PCT -£1,759,126
2. Lambeth PCT -£1,522,949
3. Wandsworth PCT -£1,442,211
4. Southwark PCT -£1,173,308
5. Newham PCT -£1,049,657