Plans for polyclinics would mean the closure of as many as 1,700 surgeries in England, the Conservative Party has claimed.
But the party was forced to admit its own plans could also destabilise practices, by allowing them to go bust.
A Conservative analysis showed that the polyclinic plan would mean the closure of 1,091 practices in London, or 71 per cent of surgeries. Some 609 (9 per cent) would be at risk elsewhere in the country.
The party's figures on polyclinic closures assume that 25 GPs would staff each polyclinic. The estimate of surgeries to close is based on this migration of GPs divided by the average number of GPs per practice in each PCT.
In a speech to the King's Fund think tank, Conservative leader David Cameron accused Gordon Brown of 'attempting what Nye Bevan never did - to nationalise general practice'.
He pledged that a Conservative government would end top-down policy impositions such as this, and allow doctors to determine the opening hours, size and location of practices.
It would also empower GPs by giving them full control over care budgets, to protect continuity of care and ensure efficient spending, he said.
But shadow health secretary Andrew Lansley was forced to admit that the plans would have a downside.
Greater responsibility for spending on patient care meant that 'it would theoretically be possible for a GP to go bankrupt', he said.
Dr Stewart Drage, a GPC negotiator and joint chief executive of Londonwide LMCs, welcomed the Conservative leader's comments. 'What you said in your speech resonates pretty well with GPs in London,' he said.
However, his GPC colleague, Dr Chaand Nagpaul, said he was concerned about the implications of a system under which GPs could go bust. 'I'd be very worried about the potential to link out-of-hours care budgets to budgets from which GPs draw an income,' he said.
Surgeries under threat
1,700 practices in England could close, Source: Conservatives
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