A strike by up to two million public sector workers in the UK has been hailed as "historic" - closing schools, courts, museums and jobcentres, and disrupting transport, hospitals and Government departments.

Unions reported huge support for the 24-hour walkout in the bitter row over pensions, but warnings of massive delays at Heathrow airport failed to materialise, with passengers saying border controls were "better than usual".

Union officials accused the Government of "ramping up" possible airport disruption and claimed that "under-trained" staff had been drafted in to cover striking immigration and passport workers.

"Some of those on duty today don't have proper security clearance. They are not qualified to do the job properly, which is a concern. We will take this up after the strike ends," said an official from the Public and Commercial Services (PCS) union.

The PCS said reports from picket lines showed a "huge" turnout for the strike, with up to 90% of staff in some Government departments, including Revenue and Customs, taking action.

General secretary Mark Serwotka said: "People should be very proud of the stand they are making today, in contrast to the shame of the Government. Public sector workers have come together today to show their united opposition to the Government's prolonged and concerted attacks on their pensions, jobs and communities."

Unite general secretary Len McCluskey, who will address a rally in London later, said November 30 would go down as the day when the union movement and workers fought to protect the economic and welfare advances of the last 60 years.

"When Francis Maude, the Government's lead pensions negotiator, can receive a pension of £43,000 a year, but nurses, teachers, dinner ladies, firefighters and librarians have to pay substantially more, work longer and receive less in real terms when they retire, the mantra of 'We are all in this together' has a very hollow and shabby ring."

Hospital employees and workers on the Mersey tunnels were among the first to take action from midnight, setting up picket lines and holding up banners attacking the Government's pension reforms.

Early Government figures suggested that almost three in four schools were affected by the walkout, although that number could rise.