Hundreds of GPs may be able to claim back thousands of pounds in seniority pay for the 2007/8 financial year, according to accountants.
GP leaders say repayments have already been made to many GPs, but urged them to double check that they have not been short changed.
A final seniority figure - a measure of average pensionable income - for 2007/8 published this month by the NHS Information Centre is lower than the interim figure used to calculate payments to GPs.
As a result, GPs who were entitled to receive full seniority pay have received a reduced amount, while other GPs may wrongly have been denied any seniority pay at all. The interim seniority figure used for England and Wales was £95,355. But the final figure for England was £90,355. In Wales, the final figure was far lower, at £78,938.
A 55-year-old GP earning two thirds of this amount per year or more would receive a seniority payment of £9,186.
Any GP earning between a third and two thirds of average income would receive a payment reduced by 40 per cent, and GPs earning less than a third of the average income would receive no seniority payment.
The artificially high interim seniority figure means the thresholds for receiving full, 40 per cent reduced, or no seniority pay were far higher than they should have been.
Laurence Slavin, a partner at specialist medical accountants Ramsay Brown and Partners, said: 'There may be GPs out there who can get some money back. GPs may have had their payments abated incorrectly.'
GPC Wales chairman Dr David Bailey said a higher proportion of GPs in Wales had been affected than in England because of the larger gap between interim and final seniority figures. He said repayments had been made, but urged GPs to check they had been paid the correct amounts.
2007/8 interim seniority figure for England and Wales
Value of full seniority pay by age
Age: Seniority entitlement