The UK is experiencing some of its worst disruption to services in decades as more than 2 million public sector workers stage a nationwide strike, closing schools and bringing councils and hospitals to a virtual standstill.
The mass strike by 29 unions over cuts to public sector pensions started at midnight and was billed by the TUC as the biggest stoppage in more than 30 years, comparable with the last mass strike by 1.5 million workers in 1979.
Unions said early indications were that the walkout was being solidly supported and predicted that 30 November would go down in history as the biggest day of industrial action since the 1979 Winter of Discontent.
Brendan Barber, the TUC general secretary, said public sector workers were suffering "real injustice" at the hands of the government.
"There will be some disruption to services as a result of the action – we regret that. But an awful lot of public sector workers are today saying they feel they are being treated with real injustice by the government trying to force through very, very unfair, damaging changes to their pensions. And I think that message is going to come across very, very loud and clear today."
But David Cameron claimed that the industrial action was "looking like something of a damp squib".
He said the strikes were "irresponsible and damaging" and support among public sector workers had been far from universal.
"Despite the disappointment of the party opposite, that support irresponsible and damaging strikes, it looks like something of a damp squib," he told the Commons.
The chancellor, George Osborne, who delivered a fresh blow to public servants on Tuesday when he announced a further two years of pay restraint and signaled plans to end national collective bargaining, warned trade unions that the strike "is not going to achieve anything". "It is only going to make our economy weaker and potentially cost jobs," he said.
"So let's get back round the negotiating table. Let's get a pension deal that is fair to the public sector, that gives decent pensions for many, many decades to come but which this county can also afford and our taxpayers can afford. That is what we should be doing today, not seeing these strikes."
It was unlikely that many would heed his warning at such a late stage and amid widespread anger at what unions say is a "singling out" of public sector workers by the government in its drive to reduce the deficit.
The mass action will include walkouts by UK Border Agency staff, probation officers, radiographers, librarians, job center workers, courts staff, social workers, refuse collectors, midwives, road sweepers, cleaners, school meals staff, paramedics, tax inspectors, customs officers, passport office staff, police civilian staff, driving test examiners, patent officers, and health and safety inspectors.
Hundreds of marches and rallies are due to take place in cities and towns across the country.
Cabinet ministers lined up to denounce the strike action over pension changes, insisting that the deal on offer was "generous".
The Labour leader, Ed Miliband, tweeted: "I'm not going to condemn public servants who feel they're in an impossible position.
"It is the government's failure that has led to today's strike."
Unions and ministers were also locked into a row about the nature of the talks, with trade union leaders complaining at the dearth of talks in some pension scheme-specific negotiations since the latest offer was tabled – a claim the government said was "simply not true".
The mass action has led to closures and disruptions at around three in four state schools in England; cancellation of refuse collections, and the postponement of thousands of non-emergency hospital operations.
The Department for Education (DfE) said it believed that more than half of England's 21,700 state schools (58%) were closed, with a further 13% partially shut. Around 13% are open, the DfE said, while the rest are unknown.
In Scotland an estimated 300,000 public sector workers are expected to strike, with every school due to be affected after Scottish headteachers voted to stop work for the first time. Wales and Northern Ireland were also expected to be affected.
Disruptions affected road travelers, with some major roads in Tyne and Wear jammed, with queues on the A167 Tyne Bridge and slow-moving traffic on a number of other routes in the area.
But early indications suggested those using rail and airport services were not facing delays.
Airport services in southern England so far seem to be unaffected, with flights at Luton airport in Bedfordshire and Stansted airport in Essex operating normally. There were also no delays at Manchester airport. By mid-morning, Gatwick airport had received 57 inbound flights and said passengers had been passing through the border zones as normal. Heathrow airport appeared to be largely unaffected, according to passengers and staff.
Gatwick's chief operating officer, Scott Stanley, said: "While passengers have so far not experienced delays at the border zones, we do expect delays to occur at some point today as the rate of arriving flights increases. That said, we do have robust plans in place to help keep those delays at the border zones to a minimum."
Eurostar has warned passengers traveling from Paris and Brussels to London to get to their departing station well ahead of time in case of delays, but added: "So far, everything is fine, with no delays or cancellations."
The day of action takes place the day after the chancellor, fueled anger after telling MPs in his autumn statement that he was imposing a 1% cap on public sector pay in the two years from 2013 in order to pay for extra spending on schools, house building and infrastructure projects.
Osborne denied he was picking a fight with public sector workers.
"I'm not picking a fight with anyone," he told BBC Breakfast. "I'm trying to deal with this country's debts that were racked up in the good years and, unfortunately, now we are in the difficult years, we are having to pay them off." .
He reiterated the government's position that the pension offer on the table was "a very generous deal".
Pickets began to form before dawn at many hospitals, ports and colleges, at Whitehall departments and outside the gates of the House of Commons, which means cabinet ministers going into work will be coming face to face with staff angered by the pension changes..
Francis Maude, the minister for the Cabinet Office, who had appealed to public sector workers to go to work as normal, said significantly fewer than a third of civil servants were on strike.
He said the government expected around three-quarters of schools in England to be closed or partially closed during the day of union action. Council services such as refuse collection, street cleaning and libraries were also likely to be affected, he said, and passengers "may face longer than normal waiting times at airports and ports".
But he said "robust contingency plans" were in place. "Overnight the borders have been managed without any major problems, and are currently operating normally. There have already been several seizures this morning: for example, 1.5kg of cocaine seized at Stansted."
Health services will also be affected, and some organizations have had to reschedule elective surgery and outpatients' appointments so that urgent cases can be prioritized. But emergency and critical care services would be "operating normally" and 999 calls would be responded to as usual, the minister added.
"Responsibility for any disruption which people may experience today lies squarely with union leaders," he said.
Unions and employers have struck local deals to avoid disruption to emergency operations and to continue essential medical services at hospitals, mental health units and residential care units for children. Emergency rotas have been introduced by mental health social workers, with union agreement.
The health secretary, Andrew Lansley, said public servants should consider patients' interests first.
He told BBC News: "Unfortunately this [the strike] is happening at the point of course when we tend to go into winter pressures and the consequences of Christmas and New Year. It makes it harder. Not great timing. It will inconvenience patients, I'm disappointed about that."
Lansley added: "I asked staff to consider patients' interest first. I hope that many staff who have been balloted to go on strike will choose not to go on strike."