The GMC is looking forward to a £3.5 million windfall this year after it started charging almost 9,000 doctors over 65 for registration.
Five months into the year, extra payments from retired doctors have already pushed the GMC's income up by £1.5 million.
The fees windfall amounts to more than 4 per cent of the GMC's annual £83.3 million income.
The GMC scrapped exemption from its £410 annual registration fee for over-65s last year because it was breaching age discrimination laws.
It started charging around 8,900 doctors over 65 in January. Many GPs over the age of 65 wish to remain registered for occasional locum work, prescribing, or work on social security or medico-legal panels.
Dr Krishna Korlipara, a part-time GP over 65 and former member of the GMC, said it was 'iniquitous' for a 'premium fee' to be extracted from over-65s who are not practising.
He called on the GMC to look into a sliding scale based on income.Doctors pay the GMC the full registration fee unless their income drops below £21,862. They are then entitled to a 50 per cent discount.
'I would hate to see over-65s subsidising the rest of the profession,' Dr Korlipara said.
'The GMC should seriously look at the possibility of reducing the fee for over-65s just to cover costs rather than to make a profit.'
A GMC spokesman said: 'The additional income from doctors over 65 will be factored into the 2010 budget-setting process, and so it will be taken into account in determining future ARF (annual retention fee).'
The BMA appealed to the High Court to stop GPs over the age of 65 being charged late last year but lost.
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