Patients face a drastic shortfall of thousands of family doctors undermining the government's plans to speed up treatment, a new analysis of NHS shortages claims.

Up to 4,700 doctors are expected to retire in the next eight years, many of them part of a wave of Indian doctors recruited in the 1960s and now reaching pensionable age, according to figures collected by the Liberal Democrats.

And doctors' leaders accused Labour of denting hopes of future recruitment and retention by "politicising" shocking cases such as the Harold Shipman murders, using them as a stick with which to beat other GPs.

Ministers are now considering increasing their promise to train 2,000 doctors amid blunt warnings from the profession that it is nowhere near enough.

"I am fed up with people saying there is no problem in the medical workforce when frankly there is," said Dr Lawrence Buckman, of the BMA's general practitioners committee.

The Lib Dems calculate that the sudden rush of retirements - coupled with new responsibilities under the 10-year NHS plan, which the BMA estimates would require up to 10,000 more doctors - could eventually create a shortfall of up to 15,000 doctors. Family doctors can in theory work until they are 70, but on average retire 10 years earlier.

A spokeswoman for the Department of Health said ministers were working with the BMA to solve the problem.