Doctors at the BMA annual representative meeting in Harrogate warned that without urgent action, practices could be forced to close.
A university practice in Essex revealed at the conference that funding cuts had forced it to close its doors to patients on Wednesday afternoons.
GPC chairman Dr Chaand Nagpaul said: ‘There is mounting evidence that the withdrawal of MPIG is hitting practices in challenging circumstances who often deliver care to vulnerable communities.
‘These are practices that serve desperate rural communities, deprived inner city areas or universities with large, transient populations.
‘In the East End of London alone up to 12 practices are facing potential closure. The decision to phase out MPIG is turning into a disaster.’
GP reported earlier this month on a protest march in east London over the impact of MPIG cuts, in which hundreds of patients, GPs and others spoke out against the reforms.
GP has also highlighted the case of a rural Lancashire practice facing closure.
The latest to speak out against the reforms is a university practice in Essex. The Rowhedge and University of Essex Medical Practice has launched a campaign to safeguard its future.
Dr Michele Wall, a GP at the practice, said: ‘We care for some very vulnerable people, many who are away from home for the first time, with 40 per cent coming from overseas. Every October we register 2,500 new patients – the logistics are phenomenal.
‘The funding changes will see us lose close to a third of our funding and this comes at a time when like many other practices, we are struggling from rising patient demand and workload. NHS England has completely failed to help us get through this problem. I fear that unless we get proper support GP services will disappear at the University of Essex and other universities.’
Doctors at the conference carried motions expressing dismay at the impact of MPIG cuts, and highlighting that the funding top-ups were guaranteed 'in perpetuity' to protect practices.