The biggest strike for five years closed thousands of schools and disrupted courts, driving tests and jobcentres today, with warnings of fresh industrial action to come.
Hundreds of thousands of teachers, lecturers, civil servants and other workers walked out in protest at controversial changes to their pensions, which they attacked as "unfair and unjust".
Unions clashed with the Government over the impact of the strike, while labour leader Ed Miliband was told he was a "disgrace" for failing to support the action.
Mark Serwotka, leader of the Public and Commercial Services union, predicted that up to four million workers could be involved in strikes in the autumn if the bitter row is not resolved.
PCS members will start a month-long ban on overtime from midnight, which Mr Serwotka said would hit work in jobcentres, passport and benefit offices and government departments.
The PCS said it was the best supported strike it had ever held, with 200,000 taking action, but the Government put the figure at half that, saying action was "premature" while negotiations were continuing.
More than 11,000 schools in England alone were disrupted due to the walkout, according to the Department for Education (DfE).
Teaching unions suggested the numbers were higher, with the Association of Teachers and Lecturers saying that around 85% of schools were fully or partially closed across England and Wales.
Kevin Courtney, deputy general secretary of the National Union of Teachers, said the union realised the action was "very disruptive for parents," adding "we do regret that".
"We had hoped to reach a settlement before the industrial action, but the Government isn't serious about talks."
Siobhan Freegard of parenting website Netmums said parents were tolerant of the action, but that would only stretch so far.
"Tolerance is not going to stretch very far because the majority of mums now work," she said.
"One or two days are fine, and businesses understand, but a lot of people work in situations where businesses aren't going to put up with taking all these days off, and, as with snow days, start docking money."
Mr Miliband criticised workers for walking out while negotiations on reform of their pensions were still ongoing, saying that while he understood the anger of the teachers and civil servants involved, the action was "wrong" and would not help them win their argument with the Government.
Addressing the Local Government Association conference in Birmingham, Mr Miliband said that under his leadership Labour would be "the party of mums and dads who know the value of a day's education".
There was strong criticism of the Labour leader at a union rally in London where one speaker branded his stance a "disgrace" to loud cheers from the audience.
Unions said up to 20,000 took part in a huge march and rally in central London, which passed Downing street and Parliament, before a series of speakers lined up to warn that cutting pensions would force people to leave teaching or quit pension schemes.
Mr Serwotka said 85% of his members had been on strike today, MPs had refused to cross picket lines and staff in Downing Street had taken action.
"The Government has been rumbled, and ministers are either badly briefed - or they are lying. Robert Maxwell robbed private sector pensions, now this Government is trying to rob public sector pensions."
Mary Bousted, leader of the ATL said: "We are here because of our force of reason, not the Government's reason of force."
She accused the Prime Minister of "spouting nonsense" over the state of public sector pensions.
Vicky Josiah, a 22-year-old teacher from south-east London, said she was made to feel like a "villain" for defending her pension, telling the rally that many people were seriously considering leaving the profession or opting out of the pension scheme.
"I will not be able to perform the same quality of teaching if I have to work to 68 as I do now. The idea of teaching at 68 is impossible."
Cabinet office minister Francis Maude said: "What today has shown is that the vast majority of hard working public sector employees do not support today's premature strike and have come into work. I want to thank them all for coming in, ignoring the pickets and putting the public first.
"I am not at all surprised by the very low turnout for today's action - less than half of PCS's own members chose to take part. Very few civil servants wanted this strike at all - less than 10% of them voted for it - and they are right.
"It is simply wrong for their leader to be pushing for walkouts when serious talks, set up at the request of the TUC itself, are still ongoing.
"Reform of public sector pensions is inevitable, but we will ensure that public sector pensions will still be among the very best, with a guaranteed pension which very few private sector staff now enjoy.
"But they will be paid later because people live longer, and public sector staff will pay more, for a fairer balance between what they pay and what other taxpayers pay."
Downing Street said there had been "minimal impact" on the public from the strike action.
"Our border controls are in place and JobCentres and pension offices are open for business," said a spokeswoman.
Protests were held in around 80 towns and cities across the UK, while prison officers and anti tax avoidance group UK Uncut also took part in demonstrations.
A total of 37 people had been arrested in London by late afternoon for a variety of offences including possession of drugs, criminal damage, breach of the peace and an alleged breach of a bylaw at Trafalgar Square.
One police officer and six members of the public have been injured but Scotland Yard said scenes have been "largely peaceful".