The number of doctors referred to the GMC in February was the highest in a single month for 'several years', the regulator has revealed.
February saw 52 doctors referred for a fitness to practise investigation. Almost one third were GPs.
This flood of referrals is the 'highest number ... for several years,' GMC chief executive Niall Dickson told council members.
The sharp increase is 'well beyond that which we had anticipated and involves serious cases'. Mr Dickson added: 'We are not saying these are inappropriate.'
Most of the referrals are from the NHS and other public authorities, not from patients.
The rise in referrals comes on the back of a 20 per cent increase in 2009 and continues an upward trend since 2007.
Mr Dickson told the council: 'While we can speculate about why this is happening, the reality is that we cannot be sure.'
Previously it was thought that the rise in referrals could be due to NHS bodies clearing their decks before revalidation.
GMC chairman Professor Peter Rubin said in September last year: 'It is likely to be a precursor to the introduction of revalidation. Employers are beginning to take stock.'
Mr Dickson said it was 'reasonable' to wonder whether talk of revalidation had prompted people in clinical governance positions into action.
The unexpected rise means doctors are now waiting longer for their cases to be heard.
In February, only 55 per cent of doctors' hearings started within nine months of referral, down from 94 per cent in December 2009.
The GMC missed by a large margin its self-imposed nine-month wait target of 90 per cent.
One way the GMC is coping with the flood of referrals is by trying to shorten the length of hearings.