The NHS is at risk of a "brain drain" and hundreds of surgeries face closure if older family doctors are not retained, the Royal College of GPs (RCGP) has warned.
The doctors' membership body said some 594 practices across the UK, including 467 in England, are at risk of closing because three quarters or more of their GPs are aged 55 or over.
RCGP chairwoman Professor Maureen Baker has written to Health Secretary Jeremy Hunt to urge him to make retaining the older workforce just as much of a priority as recruitment.
She also warned that a pledge to boost GP numbers to 5,000 by 2020 in NHS England's General Practice Forward View could not be achieved through recruitment drives alone.
Her calls echo those of other GP leaders who have said excessive workloads are affecting doctors, who are increasingly turning to part-time work.
Prof Baker said: "Older GPs have so much to give to their patients, their colleagues and the wider NHS, yet we are at risk of 'brain drain' on a massive scale. Even with the significant levels of investment promised in NHS England's GP Forward View, this cannot be replaced overnight, if ever.
"Many GPs approaching retirement want to keep on practising but also want to develop other interests, medical and otherwise. But there are currently very few opportunities for them to do this, without leaving the profession altogether.
"At a time when patients in some areas of the country are waiting up to a month for an appointment and people are living longer but with many and complex long term conditions, this is a tragic waste of talent and expert knowledge.
"If we fail to address this, the consequences for the health service could be dire - and it is patients who will ultimately bear the brunt by not being able to see their GP when they need to."
Prof Baker outlined a five-point plan in her letter, which includes a scheme of flexible working for older doctors, a bursary scheme to help GPs meet the costs of indemnity and a review of pension arrangements to ensure they are not a disincentive.