Up to 30,000 members of the Public and Commercial Services Union are protesting at Westminster's pension reforms.

The union's Scottish Secretary, Lynn Henderson, said the changes, which appeared in April's pay packets for the first time, were costing some members up to £150 a month.

She said workers were "very angry" and she expected strong support for the strike.

Other Government departments that will be affected include tax and benefit offices, courts, coastguards, some tourist attractions, civilian workers at the Faslane nuclear base and the Scottish Parliament.

Ms Henderson said there would be pickets at Government buildings and rallies in Glasgow and other Scottish cities.

Some health workers, mainly porters and technicians from the Unite union, are also expected to take action.

In England, the strike will be more widespread, with 400,000 expected to take part including lecturers, health workers, Ministry of Defence staff and immigration officers.

PCS figures from last year show the average civil service pension was £6000, and for lower-paid staff it was around £4200. Average pay was £22,850 a year, and 63% of civil servants earned less than £25,000.

Ms Henderson said: "Since this was introduced our members are already losing between £60 and £150 per month. It won't go to their pensions but straight to the Treasury."

STUC general secretary Graeme Smith said the action demonstrated the frustration people were feeling.

"People feel aggrieved at being asked to pay more, having to work longer and get less at the end of the day," he said.

However, CBI Scotland director Iain McMillan said: "Public-sector workers should be grateful taxpayers are still willing to pay for pensions that in many cases are better than their private sector counterparts."