The Government was tonight facing the biggest outbreak of industrial unrest since the 1979 Winter of Discontent after members of the largest public sector union voted in favour of strikes in the bitter row over pensions.
Unison said its members, ranging from school dinner ladies and refuse collectors to social workers and NHS staff, backed a campaign of industrial action by 245,358 votes to 70,253, in a 29% turnout.
The union is now set to strike on November 30, when teachers, civil servants and other public sector workers will also be staging a walkout in protest at the Government's plans to increase pension contributions.
Over 220,000 teachers belonging to the NASUWT will start voting tomorrow on industrial action, while other unions will announce the result of their ballots in the coming weeks.
The Government said Unison's voting figures showed there was "extremely limited support" for strikes, adding that the NHS had contingency plans in place to ensure quality of patient care was not compromised.
Downing Street said the strike vote was "disappointing, unnecessary and potentially damaging".
A No 10 spokeswoman said: "We have a good deal on the table - one that is fair and affordable - and we would urge the trade unions to reconsider and look at the deal on the table."
Unison's ballot was the biggest in union history, with 1.1 million voting papers sent to its members, including nurses, teaching assistants, social workers, care assistants, paramedics, police staff, school dinner ladies, probation officers, cleaners and other public sector employees.
General secretary Dave Prentis said: "The decisive 'yes' vote in the ballot reflects the deep concern that our members have over Government ministers' proposals for their pensions.
"Yesterday's statement in Parliament was a marked improvement on earlier proposals. But it is important to understand that the statement has to be translated into offers in the scheme specific talks.
"We still have had no offer in those negotiations, where such an offer can legitimately be made. We support the TUC day of action on November 30, but will be negotiating right up to then and beyond to get a fair deal for our members."
Unison said its members in local government voted by 171,428 in favour of strikes, with 54,500 against, in a turnout of 30%, while NHS workers backed action by 73,930 to 15,753 in a 25% turnout.
Union officials speculated that between two and three million public sector workers could be on strike on November 30, making it the biggest day of industrial action since the Winter of Discontent in 1979 and even rivalling the 1926 General strike.
Cabinet Office Minister Francis Maude said: "We listened to the concerns of public sector workers about their pensions and yesterday responded with a new generous settlement which is beyond the dreams of most private employees. I urge the trade unions to devote their energy to reaching agreement and not to unnecessary and damaging strike action.
"Today's Unison ballot received a very low turnout - with less than a third of their members even voting - which shows there is extremely limited support for the kind of strike action their union leaders want.
"But it is extremely disappointing that some union members are still planning to lose a day's pay and go on strike.
"I appeal to them to visit the Treasury website and read about the generous offer we have made before they take to the streets.
"These new generous protections represent a very big move. They include a more generous 'accrual rate' and protections for anyone within 10 years of their pension age.
"The settlement will see public service workers getting a guaranteed benefit in retirement, not subject to market fluctuations or fees - something which has all but been eliminated elsewhere.
"It is now time for the unions to respond in a responsible manner. The new deal is conditional on agreement being reached in scheme by scheme talks with the unions."
A Department of Health spokesman said: "We urge all NHS workers to think carefully about the effect of any action they may be considering on patients. Pensions are important to everyone - but patients should come first."
Dean Royles, director of the NHS Employers organisation, said: "This 'yes' vote is disappointing for the NHS but the majority of staff did not vote.
"NHS staff are passionate about the care of patients and are reluctant to withdraw their labour.
"This is reflected in the low number of NHS staff turning out.
"If on this turnout, the unions did decide to press ahead, that would cause delays in treatment and distress to patients.
"I would urge all sides to keep on talking and we will play our part in that.
"It is premature to consider industrial action before discussions have concluded, particularly with a revised offer newly on the table."
Neil Carberry, the CBI's director for employment, said: "For all of Unison's rhetoric about this being the biggest ballot in their history, less than a third of their members bothered to vote.
"It is disappointing that the public and businesses are now faced with the unnecessary disruption of a strike which is going ahead when just 22% of the balloted workforce supported it."
Simon Walker, director general of the Institute of Directors, said: "Yesterday's offer from the Government was designed to avert strikes, but just one day later, it looks as though this bribe has failed.
"The unions have the Government over a barrel. Once you start offering concessions, when do you stop?
"The original reform proposals were the bare minimum needed to put public sector pensions on a sustainable footing.
"Yesterday's more generous offer was a bad idea and should now be taken off the table."