Two million public sector workers in Britain went on strike on Wednesday over changes to their pensions in the biggest walkout for decades, closing thousands of schools and disrupting transport. Three-quarters of schools were estimated to be closed during the 24-hour strike, hospitals were operating with skeleton staff and local authorities were paralysed. Striking workers picketed public sector buildings in central London and more than 1,000 demonstrations were expected to take place across Britain in scenes reminiscent of the 1970s. Fears of long delays at London\'s Heathrow airport, one of the world\'s busiest air hubs, failed to materialise on Wednesday morning as two-thirds of immigration officials turned up for work. The strike is the biggest test so far of Prime Minister David Cameron\'s Conservative-Liberal Democrat coalition 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 slashed Britain\'s growth forecasts. Osborne infuriated the unions by announcing a new two-year, one-percent cap on public sector pay rises. On Wednesday, Osborne said the strike would only harm the economy, and called for unions to return to the negotiating table. \"The strike is not going to achieve anything, it\'s not going to change anything,\" the Chancellor of the Exchequer told BBC television. \"It is only going to make our economy weaker and potentially cost jobs. \"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.\" But Brendan Barber, general secretary of the Trades Union Congress (TUC), said the public sector was \"under attack\" from the government and the strike was fully justified. \"There comes a time when people really have to stand up and make a stand,\" he told ITV. \"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 ($4,650, 3,500 euros) a year. Could you live on £3,000 a year?\" At Heathrow Airport, passengers arriving on early morning flights from Australia and the United States reported few problems, despite prior warnings that delays of up to three hours were likely. A British Airways spokesman said: \"We\'ve had a positive start to the day and queues are pretty much as normal. \"There are reports that around two-thirds of the Border Agency staff are working at Heathrow.\" Elsewhere, the light rail train system was closed down by the strike in Newcastle, northeast England. A giant union rally was to take place in the industrial central city of Birmingham and in Scotland, 300,000 workers were expected to walk out. Under the government\'s proposals, public sector workers will be asked to work until they are 66 and increase their pension contribution payments. The government also plans to peg pension payouts to the Retail Price Index rate of inflation rather than the higher Consumer Price Index measure as it seeks to address the dual challenge of increased life expectancy and a depleted public purse. Staff also face a lower pension payout, based on their average salary as opposed to the final salary schemes to which they are currently tied.