David Cameron has provoked the wrath of GPs by moving to hand them responsibility for increasing out-of-hours care.
The Tories were accused of trying to reverse moves that had improved patient care and the recruitment of doctors.
In what could result in a bruising clash for Mr Cameron, on the eve of the Conservative Party's annual conference, he will promise to improve weekend and evening care by renegotiating the GPs' contract.
The Tory leader will blame the decline in out-of-hours access to family doctors on the decision to put it in the hands of primary care trusts in the 2004 contract.
"Many PCTs have, because of their own deficits, been unable financially to commission enhanced access for GPs, including evening and weekend surgeries," a new Conservative policy document says.
The announcement comes as Health Secretary Alan Johnson is calling on GPs to work more outside of the nine-to-five routine.
The Tories admit they would not be able to revert to the previous personal obligation on GPs to provide out-of-hours services but they believe that giving them a commissioning role would improve the situation.
"GPs, as budget-holders and primary care commissioners, will be in a position to respond to the interests and wishes of their patients," the document adds.
But Dr Laurence Buckman, chairman of the BMA's GPs committee, said the Tories had "failed to understand" why a new contract had been needed. "Recruitment was at an all time low, and doctors were thinking of taking early retirement because of the unsustainable workload," he said.
"It was not safe to ask exhausted GPs to work nights and weekends as well as in the daytime. The new GP contract has delivered better quality of care with pay linked to the standards of services provided."
