David Reilly and John Meyrick Thomas, who both work at Watford General Hospital, which has been fraught with difficulties since the start of the National Health Service changes, say new referrals would have to wait an unacceptably long time for surgery and they are asking GPs to refer them to other hospitals.
The types of patient deemed urgent by GPs would include those with suspected cancer, severe pain and cadiovascular conditions who need to be assessed by a specialist within a few days.
Mr Reilly, a consultant vascular surgeon, and Mr Meyrick Thomas, a gut specialist, say they have been allocated insufficient operating time for emergency and urgent cases which means they cannot offer the urgent patients surgery quickly enough after the first outpatient appointment.
GPs in south-west Hertfordshire received the letter yesterday. The surgeons say: 'In the interests of patients for whom we are unable to offer unacceptably timely care, we feel the only safe way for you to manage urgent cases is to refer them elsewhere.
'We are very sorry that the mismatch between government funding and patient need has forced this action. We very much hope that a financial solution can be found that will enable the necessary facilities to be provided.'
They say they need to be able to work in theatre for whole days rather than for sessions of a few hours.
A spokesman for North Thames Health Region said 70 per cent of GPs in south-west Hertfordshire were fundholders and they had not bought as many services from Watford as estimated. Watford General Hospital amalgamated with Mount Vernon Hospital to become a trust in April.
The spokesman said: 'The merger of the two hospitals means greater flexibility and surgeons are meeting next week to discuss working arrangements.'