As far as I can see from the letter I got yesterday from those nice people at Xaffinity Paymaster who think they may have inadvertently given me too many of the Queen's shillings, any adjustment required will be tiny. It might be bigger for those who are older and have been in receipt of pension for longer.
It seems that the error is in the annual pension increases due to the way increases were applied to the Guaranteed Minimum Pension (GMP). Due to an admin cock-up both State pension and Service pension were paying the same increase.
So it was not much help knowing what pension one was entitled to on retirement because the errors are in the annual increases awarded.
More startling is the revelation that those errors and the overpayments are to continue until April - very generous, thankyou Xaffinity - Happy Christmas!