Tens of thousands of retired public sector workers received an unwanted Christmas gift from the government this week - a letter warning them their pensions will be cut from next April.

The reductions are being made after ministers uncovered evidence that overpayments totalling up to £140m had been made for 30 years across a number of schemes including the NHS, teachers, the armed forces, the judiciary and the civil service.

The government is not going to claw back the money but says the "correct" pension payments will be made from April - which means at least 95,000 former public sector workers will have their pensions cut, or increased by less than the value of inflation.

Most of those affected should have received a letter already. If you are not contacted by Christmas, you can assume your pension is in the clear.

The obvious question many people who get a letter will be asking is: How much is my pension going to fall? Unfortunately, it appears it is not possible for the powers-that-be to give any precise answers. More information will be provided in the New Year, as it will vary from person to person.

If you are receiving a widow's or widower's pension, you may be affected. As these are based on the entitlement of the late spouse, those involved will face a lower retirement income.

The overpayments "bill" works out at an average of £1,300 per person or £3.70 a month over that period, but exact amounts will vary depending on when an individual retired and how much they were earning over the years.

It is not known if the problem affects people retiring in every year since 1978 (the year the cock-up dates back to). The scheme administrators, HM Revenue & Customs and the Department for Work and Pensions are still investigating what happened. But it seems likely that the 95,000 are spread across retirement years and salary levels.

The overpayment was first brought to light by the Lib Dems' Treasury spokesman, Vince Cable, in the Commons on Monday. Cable reported he had been in discussion with the cabinet secretary, Gus O'Donnell, about the overpayments made by the privatised company Xafinity. They were "an error of the system" and not Xafinity's fault, says a government source.

Perhaps, not surprisingly, opposition politicians accused ministers of condemning thousands of older people to a Christmas of "uncertainty and fear" after the scale of the problems emerged.

Shadow treasury secretary, Philip Hammond, says it is unacceptable that most of the individuals - some 5% of the total UK public sector pensioners - will not know what their new income is until next year.

"It is completely unacceptable for the government just to tell pensioners they have been affected but refuse to give them the full facts," he adds.

There are fears that many of the could be left struggling to make ends meet, with sharp cuts in interest rates and share values having already reduced their income from savings.

guardian.co.uk © Guardian News & Media Limited 2009 | Use of this content is subject to our Terms & Conditions | More Feeds