February saw 52 doctors referred for a fitness-to-practise investigation, the ‘highest number [of referrals] for several years', the GMC said.
The steep rise involves serious cases and is ‘well beyond that which we had anticipated', chief executive Niall Dickson told Council.
Most referrals are from the NHS and other public bodies, not from patients.
The rise in referrals comes on the back of a 20% increase in 2009 and continues an upward trend since 2007.
GMC chief executive Niall 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.
The unexpected rise in referrals means that doctors are now waiting longer for their cases to be heard. In February only 55% of doctors' hearings started within nine months of referral - missing by a large margin the GMC's self-imposed target of 90%.
‘There will be a shortish period when we won't hit our target,' Mr Dickson admitted.