The GPC said the speed with which reviews were being completed showed how desperate cash-strapped NHS organisations were to get their hands on GP funding.
In some areas, agreements have been reached to shift practices on to GMS contracts with a correction factor-type payment.
In others, NHS England's area teams are proposing a similar process to the seven-year phased MPIG withdrawal.
Some practices and LMCs are yet to hear anything about the reviews from their area teams.
30% funding cuts
The reviews could leave some practices facing 30% funding cuts for the same workload, London GP leaders said.
Londonwide LMCs medical director Dr Tony Grewal said PMS practices in the capital could face an imposed London-wide PMS contract, rather than sector or borough based deals, ignoring local variation. The deal in London could force practices to offer services seven days a week to maintain existing funding.
Local PMS reviews have been initiated across the country following the conclusion of NHS England's national review in February, when it handed control of the process to area teams.
It gave them two years from 1 April 2014 to complete local contract reviews and to decide 'how far to redeploy any premium funding and on the pace at which redeployment takes place'.
Premium funding worth £325m
NHS England identified £325m of funding above GMS equivalent, including £258m which 'may be associated with enhanced services or populations with special needs, but is not defined'.
GPC deputy chairman Dr Richard Vautrey said he was concerned over the pace at which the reviews were being carried out.
'It sends a signal as to how keen the area team is to get its hands on this money because no other funding is available,' he said.
Dr Grewal said the London PMS deal might involve a global sum equivalent based on the GMS capitation payment of about £72 a patient per year. 'Your worst-case scenario - you could be looking at a 30% loss for doing the same amount of work.'
Additional funds could be available for work towards key standards being drawn up for London, potentially including seven-day opening.
Dr Vautrey said attempts to tie PMS premium funds to seven-day access would be 'a disaster'. PMS funding, he said, had been used by practices to support core activity in core hours.