Following increased scrutiny of doctors by HM Revenue and Customs (HMRC), some locums registered as self-employed have been deemed 'disguised employees' of the practices they work for.

More than 28,000 doctors received letters from HMRC under a tax amnesty last year that recovered £9 million although only 1,500 doctors came forward.

Many of the irregularities HMRC has since discovered involve locums, accountants warn. Locums found to be 'disguised employees', and their practices, are liable to pay back tax plus interest, said Andy Fahey, partner at specialist accountants Brookson's.

He said: 'Some practices pay locums using contracts called "employment contracts" which means they fall foul of HMRC at the first hurdle. If you look or act like an employee, you are liable. Many practices keep employed GPs on as locums to avoid having to organise their tax and holiday pay.'

Dr Richard Fieldhouse, chairman of the National Association of Sessional GPs, said existing GP training was not 'fit for purpose' because it does not teach GPs about being self-employed.

'Around a quarter of GPs are now locums, so it's ridiculous that the GP curriculum teaches GPs about working as partners and salaried GPs, but not locums,' he said. 'Being ignorant of the law is no excuse. But practices are also not good at engaging their locums and employing salaried GPs.'

He added that the employment status of locums was 'just not something practices think about'.