Airline passengers arriving in Britain escaped chaos early Wednesday despite dire predictions of long waits, as border staff joined teachers, hospital workers and weather forecasters in the country's largest strike in decades.

The one-day strike has been called to oppose government demands that public sector staff work longer before receiving a pension and contribute more money each month _ plans which form part of a package of austerity measures designed to get a grip on the country's high borrowing levels.

Labor unions said as many as 2 million public sector staff were joining the strike, which would make it the largest since the infamous industrial dispute known as the Winter of Discontent in 1979, which presaged the arrival of Margaret Thatcher as prime minister.

Protesters were also denouncing sharp public spending cuts, which on Tuesday saw the government extend pay curbs further. Following the completion of a current freeze on public pay next year, pay raises will be limited to 1 percent through 2014.

London's Heathrow Airport and scores of airlines had warned that international travelers could be held in lines for up to 12 hours at immigration halls as a result of staff shortages. But airport managers said flights arriving early Wednesday from the United States, Asia and Europe were largely unaffected, in part because of contingency plans which saw bureaucrats drafted in to staff border desks.

"Immigration queues are currently at normal levels," Heathrow's operator BAA said in a statement. "However, there still remains a possibility of delays for arriving passengers later in the day."

Britain's government said less than a third of government civil service staff had walked out and that more staff than expected had showed up for work at ports and airports.

However, more than half of England's 21,700 state schools were closed, and around three-quarters of schools in the U.K. could eventually be forced to shut early, the Cabinet Office said.

Some protesters wore red T-shirts that read, "Get Angry and Fight Back," a variation of the British wartime propaganda poster, "Keep Calm and Carry on."

Announcing an extension of austerity measures, Treasury chief George Osborne said Tuesday the age for collecting state pensions would be raised to 67 in 2026, earlier than previously planned.

The decision followed an official forecast which marked down Britain's predicted growth to a feeble 0.7 percent next year, from the previous 2.5 percent prediction made in March.

Eleanor Smith, president of UNISON _ the country's largest trade union which represents about 1 million health, education and law enforcement staff _ said many of those joining the walkouts were striking for the first time.

"The government wants us to work longer, pay more and at the end get less. How fair is that?" said Smith, who joined a picket outside Birmingham Women's Hospital in central England, where she works as a theater nurse.

John Kelly, a professor of industrial relations at the Birkbeck University of London, said the strike was likely to be Britain's largest one-day walkout since the early 1970s. If the numbers exceed 2 million, it could match the 1926 General Strike, he said

"For most people, the size of this strike will be unprecedented in their lifetime," said Kelly.

Maria Haverton, 36, a hospital worker, said joining the strike had been a last resort. "We realize the government is having budget problems, but why didn't they see this coming a long time ago? I'm worried about my pension. I'm worried about my son's future," she said, close to London's King's Cross rail station.

Others stood outside publicly funded universities, complaining that education in Britain was already suffering with the cuts.

"It seems like the sectors that need to be protected the most _ education and health _ are the ones being the most affected," said Holly Smith, 28.

Health officials said 60,000 non-urgent operations and appointments had been postponed in advance in England, while in Scotland at least 3,000 operations and thousands more planned appointments were canceled.

Botanists, nuclear physicists and catering staff at the Houses of Parliament _ who formed picket lines outside the famous building _ also joined the strike, while off Britain's northernmost tip, ferry services were suspended to the Shetland Isles as a result of the action.

However, at ports and airports, the initial impact on services appeared limited.

Debbie Arnell, a 42-year-old apprenticeship assessor from Bournemouth, southern England, arrived at Heathrow early on Wednesday after a holiday in Philadelphia, and said conditions were good.

"I have used this terminal seven times before and today was better than usual," she said. "They were even giving out free fruit and water, which they don't usually do. It's almost like they have overcompensated."

Osborne has insisted the government cannot back down over the pensions dispute. A recent government report found taxpayers contribute about 32 billion pounds ($50 billion) each year to public sector pensions, and warned the gap between contributions and payments could rise to 9 billion pounds ($14 billion) by 2015.

"The strike is not going to achieve anything, it's not going to change anything," Osborne said. "It is only going to make our economy weaker and potentially cost jobs."

Ministers say some low-paid public sector workers will actually have improved pensions under the planned changes, while almost all staff will enjoy better terms than people in the private sector.

Earlier this week, Education Secretary Michael Gove accused militant labor leaders of ignoring Britain's economic reality and spoiling for a fight with the government _ evoking ex-Conservative Party leader Margaret Thatcher's battle with unions during the 1984-1985 miners' strike.

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Associated Press Writer Paisley Dodds in London contributed to this story.