Teachers, day care workers, refuse collectors, ambulance staff will be among the two million public sector workers who could strike across the UK, with more than 1000 demonstrations expected over pensions. About 35,000 hospital workers – including doctors – will also abandon their jobs for the day.

At Heathrow Airport, Immigration checks will be hampered, so passengers should expect to have to wait for anything up to 12 hours. However, a spokesman said hundreds of office-based staff have undergone training and will be out to help.

Unions behind the strikes object to the government’s plans to make their members pay more and work longer to earn their pensions. The government has in turn accused union leaders of wanting to “wreck” the economic recovery and has warned the strike, the country’s largest in decades, could prompt tougher laws on industrial action.

Out of London’s 32 boroughs, 29 said they are aware of up to 1220 council-run schools closing on Wednesday. More than 160 will be partially closed, but 84 schools will remain open. The council leader at the Labour-run Barking and Dagenham Council, Liam Smith, said in a statement: “I will not cross any picket lines.”

The London Ambulance Service has assured it would still deal with emergencies, but said it would prioritise the “most seriously ill and injured patients”. These include patients who use LAS transport service to attend pre-arranged hospital appointments for cancer treatment and dialysis.

Similarly, NHS London said it was in discussions with unions to ensure hospitals had “sufficient safe cover”.

The British Museum said it may close on Wednesday, but Tate Modern, Tate Britain, the Science Museum and the Natural History

Museum said they would remain open.

In this escalating row workers oppose government demands that they work longer before receiving a pension, contribute more money each month and accept a pension calculated using their average career salary, rather than their final salary. Ministers insist that Britain has no option but to reform its pension system because people are living for longer, and because the gap between contributions and pension payments is growing.

Treasury minister Danny Alexander has urged labour unions to accept a deal proposed by the government, which includes some concessions for low earners and those within 10 years of retiring.

“I reserve the right to take those enhancements off the table if an agreement can’t be reached,” Alexander was quoted as telling

The Guardian newspaper on Saturday. “I don’t want to do that. I don’t want to be in that position. I want to be in a position where we have got an agreement.”

Brian Strutton, the national secretary of the GMB labor union, which represents about 600,000 local government and health sector workers, said the government appeared more interested in issuing threats than negotiating a resolution.

“Only a last minute breakthrough in negotiations can stop the strike but that isn’t going to happen if we are not even meeting,” Strutton said.

The walkout is expected to top the scale of Britain’s 1979 strikes — when tens of thousands of people halted work over pay disputes. Some labor unions claim the action could even eclipse Britain’s 1926 general strike, when about 1.75 million people joined walkouts.