GPs could be forced to pay for their own revalidation, the GPC has warned.
The system will throw up substantial costs, both directly and through clinician hours lost to the NHS.
GPC chairman Dr Laurence Buckman last week expressed concerns about the unknown cost of the policy.
'I have been asking who will pay for this process for the past 10 years, and I have never had an answer,' he said.
He added that GPs may have to pay for their own revalidation, pointing out that PCTs had already refused to fund appraisals for sessional GPs.
Dr Buckman also said he was concerned sessional GPs would struggle to obtain the feedback necessary for their appraisal.
Revalidation 'is going to be a problem for people who don't have a (single) place of work because you are not always in the same place long enough to have multiple sources of feedback,' he said.
RCGP chairman Professor Steve Field said revalidation could be problematic for private doctors, postgraduate deans and doctors on cruise ships as well as for sessional GPs.
He admitted doubts would remain over funding until the system had been fully designed.
'The GPC is right to raise it as a concern,' he said. 'But because we don't know what the system looks like yet, we just don't know,' he said.
The minutes of the first meeting of the UK Programme board, on 10 February, suggest it did not discuss how to fund the system.
The GMC-led board, which will oversee the roll-out of revalidation across the UK, is in the process of interviewing companies to pilot revalidation.
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