Union leaders have warned the government that industrial action will continue into next year after a strike by over a million public sector workers caused widespread disruption to schools, councils and the fire service.
Officials said they were "overwhelmed" by the strength of support for the walkout, sparked by a series of bitter disputes with the coalition over pay, pensions, jobs and spending cuts.
At a huge rally in central London, unions made it clear the action would continue into the New Year, stretching to the run-up to the general election.
They also hit back at Conservative plans to change balloting laws as "utter hypocrisy".
The government said fewer than half a million took part in today's action, but the six unions which organised the strike described the figure as "laughable".
The GMB said more people were on strike than just union members, putting the total at well over a million.
Schools across England and Wales closed and there was disruption to council services, museums and galleries, the fire service, courts, driving test centres, libraries and jobcentres.
Across 66 local authorities in England almost 3,000 schools, nurseries and colleges were reporting that they had been affected by the walkout, with some forced to close entirely.
Many of these figures did not include academies, which are not under local council control.
Caretakers, teaching assistants and other school staff took part in the action, alongside teachers.
Telephone callers to jobcentres were told in a recorded message that a limited service was available because of "service difficulties".
Picket lines were mounted outside courts, council offices, jobcentres, fire stations and Parliament in outpourings of anger over the coalition's public sector policies.
The Prime Minister and other senior politicians attacked the strikes, arguing that they were based on ballots conducted some years ago which saw low turnout from union members.
The Conservatives are drawing up plans to change employment law so that a threshold of those balloted would have to be reached before industrial action could be held.
But Unite said no Tory Cabinet member achieved a 50% voting threshold in the last general election.
General secretary Len McCluskey said: "It is utter hypocrisy for the Government to talk about mandates for trade unions when not a single member of the present Cabinet would have been elected using the same criteria.
"The fact is not a single councillor in England has won 50% of the electorate, not a single MEP has reached the 50% threshold, Boris Johnson (London mayor) scraped in with just 37% in 2008 and the Government's flagship police and crime commissioner election gained a risible 17% of the vote.
"This Government has no mandate to attack trade unions or the workers who have been forced to take industrial action today in their fight to end poverty pay."
A study by Unite showed that the Cabinet member with the lowest percentage of the vote was Welsh Secretary David Jones, who secured the support of 27% of the electorate in his seat of Clwyd West in 2010, and Culture Secretary Sajid Javid achieved a vote of 30.8% of the electorate in his constituency of Bromsgrove in 2010.
Mr McCluskey added: "Britain's anti-trade union laws are already amongst the most restrictive in Europe.
"Tory attempts to further curtail the rights of working people to democratically organise risks placing Cameron's Britain alongside nations like Kazakhstan, Albania and Niger, where the right for public servants to take action is forbidden."
Unison said the strike was particularly well supported in the North East, Wales and East Midlands where the union said most council offices were closed, adding that more than 60 picket lines had closed the majority of services in Newcastle.
On the south coast and Wales, delivery vans had refused to cross picket lines.
In London, strikers mounted more than 150 picket lines with many workers refusing to cross.
Unison general secretary Dave Prentis said: "It is a massive decision by local government and school support workers to sacrifice a day's pay by going on strike, but today they are saying enough is enough.
"It is a scandal that people who educate and support children in schools, maintain crucial local services, keep our communities clean and safe places to live, and protect the homeless and vulnerable are not paid at least the Living Wage."
National Union of Teachers general secretary Christine Blower said: " I've been getting messages from people saying that they are more determined now than they were in the past to take action."
Ms Blower insisted that industrial action was just one part of their "stand up for education" campaign, which also included informing and working with parents and lobbying politicians.
"There are 1,000 teachers in every constituency and politicians need to start listening and begin to put pressure on the Government themselves," she said.
The NUT's action, which focuses on three issues - pay, pensions and working conditions - has been condemned by the Department for Education (DfE), which said that it would hold back pupils' education.
"There is no justification for further strikes," a DfE spokeswoman said.
"The unions asked for talks, we agreed to their request and talks are ongoing.
"The Secretary of State joined talks with the unions on June 25 .
"All ministers meet with the unions frequently and will continue to do so.
"These strikes will only disrupt parents' lives, hold back children's education and damage the reputation of the profession."
Mick Cash, acting general secretary of the Rail, Maritime and Transport union, warned of wildcat strikes if changes were made to balloting laws.
"If you remove the right to strike legally or make it almost impossible, then workers will, understandably, take matters into their own hands."
The TUC has said public sector workers were on average more than £2,000 worse off under the Government, while half a million council employees earned less than the living wage.
At the rally in Trafalgar Square, Matt Wrack, leader of the Fire Brigades Union, said more strikes should be held "soon."
"What we see today is an inkling of the power that rests in the hands of working people," he said.
"We have a government destroying our public services and wrecking the lives of public servants.
"This is our 15th strike, and we are not giving up.
"There is no mood to surrender, but there is a mood to continue the fight."
Mark Serwotka, leader of the Public and Commercial Services union, said the way public servants had been treated by the coalition was an "absolute disgrace", although he also criticised the Labour Party for "looking the other way".
Labour leader Ed Miliband said: "Nobody wants to see these strikes because of the disruption that is being caused for parents and others.
"Strikes are always a sign of failure on all sides but the key now is to prevent further strikes and further disruption happening.
"When the government is today ramping up the rhetoric against public service workers demonising them even more I don't think that's the answer.
"The answer is to get round the table and prevent further strikes happening."
Cabinet Office minister Francis Maude said: "We want to thank the vast majority of public servants who turned up for work as usual today.
"Our official estimates are that fewer than half a million took part in this strike action - well short of the inflated claims of union leaders.
"Within the Civil Service, there has been the lowest recorded turnout for a national strike.
"Every jobcentre opened, the majority of children went to school as normal and fire services continue to operate with robust contingency arrangements in place.
"As part of our long-term economic plan, this Government has had to take tough decisions, including to restrain public sector pay.
"The blame for today's disruption rests with those union leaders who pushed for unnecessary strike action with weak mandates."
The PCS described the Cabinet Office's figures as "laughable", adding: "No-one can trust this government to keep reliable figures, it can't even tell us what it's done with dozens of Home Office files."
A spokesman for the Local Government Association said: "With a £5.8 billion funding shortfall to tackle over the next two years, budgets for local services will continue to be stretched for the foreseeable future.
"The offer we have made to increase most employees' pay by 1% is at the absolute limit of what local authorities can afford."
In Brighton, t eaching assistant Abi Chambers joined a rally, saying: "I'm out here because Michael Gove (Education Secretary) thinks teaching assistants don't do any justice to the children.
"We have a very important job and he doesn't realise how well the children relate to us, and how their performance matters to us.
"He's trying to get rid of us because statistic-wise we don't make a difference, but we do."
Mr Gove said the NUT's strike mandate was two-years-old and did not have the backing of the majority of the union's members.
He said the walkout was imposing "significant costs on families who have to pay out for expensive childcare or give up a day's work".
Mr Gove also backed the idea of re-examining balloting laws, saying it was important that public services were protected and that any strike "reflects the interests of those in whose name it is taken".
Around a fifth of schools in England were forced to close, according to the Department for Education (DfE), with academies much less likely to have shut than those under local council control.
A spokeswoman said: "The NUT has tried to cause as much disruption for children and their families as possible - but thanks to the dedication of many teachers and staff who turned up for work, just 21% of schools were closed today.
"That represents a huge drop on the 60% of schools which closed the last time that unions representing both teachers and support staff like caretakers went on strike."
She added that there was "no justification" for further strikes and that talks were continuing.