More than two million public sector workers are expected to go on strike on Wednesday in protest at changes to their pensions in the biggest industrial action in Britain for three decades. They argue the government is trying to make the low-paid carry the can for a crisis not of their making. Thousands of schools will be closed, refuse will remain uncollected and hospitals will have skeleton staffing. Passengers arriving at London’s Heathrow airport, one of the world’s busiest air hubs, have been warned to expect delays of up to 12 hours to have their passports checked as many border control officials will walk out. The strike will be the biggest test so far of Prime Minister David Cameron’s coalition government, which sparked the unions’ fury by proposing to bring the retirement age for public sector workers into line with the state pension. The reforms mean most civil servants, council workers and teachers will have to work until the age of 66 and most will have to pay more into their pensions only to receive a lower payout. Cameron has condemned the strike, arguing the government has made a reasonable offer on public sector pensions at a time when it is ushering in a raft of austerity measures aimed at slashing the deficit. “We have put forward, I think, a very fair and very reasonable offer in terms of public sector pensions. And I think this strike is completely wrong,” Cameron said on Monday. The leader of the Unison union, Dave Prentis, said there was “absolutely no chance” of reaching a deal in the next few days and predicted 2.6 million people could take part — making it the biggest since the 1926 General Strike.