Hundreds of thousands of British public sector workers went on strike Thursday to defend their pensions, causing widespread school closures in a major challenge to the year-old government.
Jobcentres, tax offices and museums were also closed across the country as four unions called out up to 600,000 workers to protest against plans to make them work longer and pay more into their pensions.
However, airport operator BAA said fears of delays at London Heathrow from a walkout by immigration and customs staff had failed to materialise on Thursday morning.
Prime Minister David Cameron said the strike was premature as the changes were still being negotiated, and warned that with an ageing population reform was inevitable because "the pension system is in danger of going broke".
Action by three education unions caused the closure of about a third of schools in England and the disruption of another third, according to the Department for Education. There was also widespread disruption in Wales.
Picket lines were also set up outside government buildings, law courts and even the British Museum, and several thousand people gathered for a march in London, brandishing banners calling for "Fair pensions for all".
"I will lose £60,000 (66,000 euros, ê96,000), I'll pay an extra £60 a month and I'll have to work seven or eight years longer" under the reforms, said Richard Jones, a 39-year-old civil servant on the march.
It looks set to be the largest public sector strike since one million local government workers walked out in March 2006, and some union leaders have warned it may only be the beginning of months of industrial unrest over pensions.
Cameron's Conservative-Liberal Democrat coalition has been the focal point of public sector anger after it announced a two-year pay freeze and 330,000 job losses by 2015 in an attempt to rein in a record budget deficit.
It is now facing the possibility of widespread unrest just 13 months after it took office over plans to delay the retirement age for public sector workers by up to six years, increase their contributions and replace their final salary pensions with ones based on their average career earnings.
"This is the best-supported strike we've ever had," said Mark Serwotka, the head of the Public and Commercial Services (PCS) union, which has called out 250,000 civil servants for the strike.
He said they were sending "a clear message to the government that they will not tolerate these attacks on their hard-earned pensions rights".
The biggest impact appeared to be on schools as members of the National Union of Teachers (NUT) and the Association of Teachers and Lecturers (ATL) walked out. Staff in the University and College Union (UCU) also joined them.
Education minister Michael Gove said he was "disappointed" at the action.
Ministers say the strike is premature given that talks on the reforms were ongoing, and note that Unison, the biggest public sector union with 1.3 million members, had opted to keep talking, although it may strike later this year.
Francis Maude, the minister who oversees the civil service, told BBC radio: "You cannot continue to have more and more people in retirement being supported by fewer and fewer people in work. Long-term reform is needed."
However, the unions say they have already accepted reforms over the past decade but say the government is trying to push through the new changes without any offer of compromise.
Ed Miliband, the leader of the main opposition Labour party which has historically close ties to the trade union movement, urged both sides to return to the negotiating table.
"These strikes are wrong at a time when negotiations are still going on but parents and the public have been let down by both sides because the government has acted in a reckless and provocative manner," he said.
A ComRes poll this week found 49 percent of the public believed the workers had a legitimate reason to strike.