Up to two million public sector workers in Britain went on strike yesterday over changes to their pensions, after the government responded to slashed growth forecasts with fresh spending cuts.

In what unions said was the biggest walkout in decades, thousands of schools were shut, hospitals operated with minimum staffing levels and local authorities were paralysed.

Thousands of workers marched through central London and Manchester, northwest England, during the 24-hour strike.

However, fears of long delays at London’s Heathrow airport, one of the world’s busiest air passenger hubs, failed to materialise as most immigration officials turned up for work.

Ferry ports and cross-Channel rail services linking Britain to continental Europe, also operated largely as normal.

The strike is the biggest test so far of Prime Minister David Cameron’s Conservative-Liberal Democrat government, which sparked the unions’ fury by making public sector workers pay more into their pensions and work longer.

Anger rose further on Tuesday when finance minister George Osborne targeted the pay of teachers, nurses and soldiers and revealed plans to cut an extra 300,000 public sector jobs as he sharply reduced Britain’s growth forecasts.

Mr Osborne infuriated the unions by announcing a new two-year, one-per cent cap on public sector pay rises.

Mr Cameron was scathing about the strike, telling parliament it had been a “damp squib” and lambasting unions for calling the action while negotiations on pensions were ongoing.

The Prime Minister insisted that reforms to public sector pensions were “absolutely essential”, and accused Ed Miliband, leader of the opposition Labour Party, of being “irresponsible, left-wing and weak” for refusing to condemn the strike.

The Unison union said two million workers had taken part in the stoppages, and claimed they had wider support.

Brendan Barber, general secretary of the Trades Union Congress (TUC), said the government had put the public sector “under attack” and the strike was fully justified.

“There comes a time when people really have to stand up and make a stand,” he told ITV television.

“With the scale of change the government are trying to force through, making people work much, much longer and get much, much less, that’s the call people have made.”

In Salford, northwest England, around 30 refuse collectors manning a picket line outside their depot dismissed claims that their pensions were “gold-plated” compared to those in the private sector.

Neil Clarke, a union organiser with Unite, said: “The government is attacking our pension schemes - they are looking for public sector workers to contribute more, work longer and receive less in pension benefits.

“The average public sector pension comes in at £3,000 (€3,500) a year. Could you live on £3,000 a year?”

BAA, the operator of Heathrow Airport, said queues at border control points were “normal”, despite prior warnings that delays of up to three hours were likely.

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