A strike over public-sector pension reform expected to involve more than 2 million workers will go ahead on Wednesday, a union leader said on Monday, warning of more stoppages next year if ministers refuse to negotiate on the dispute.

The action will go ahead. There is absolutely no chance whatsoever of any deals over the next couple of days, said Dave Prentis, who heads Unison, the biggest union involved which represents 1.4 million workers across the public services.

About 30 trade unions will join the strike on Wednesday, hitting public services as diverse as health, refuse and tax collection, closing thousands of schools and causing likely chaos at ports and airports as border control staff walk out.

They are protesting over the Conservative-led coalition's reforms that unions say will make employees pay more for their pensions and work for longer before they can retire. The government says reform is needed as people are living longer.

Two thirds of all schools may be forced to close on Wednesday, hitting millions of parents who are already struggling in an economic downturn.

Airlines said on Monday they are cutting flights into Heathrow, Europe's busiest airport, because of fears of long delays and overcrowding due to the passport control strike.

Prentis stressed that unions wanted a settlement, but added that they would have no choice but to move ahead with plans for more if the coalition failed to table a new offer by the end of the year.

It could involve rolling programmes, region by region, service by service, workers within particular services - nothing is ruled out at this stage, he told reporters in London.

The government, which wants public sector workers to contribute more, retire later and receive pensions based on average earnings rather than final salaries, made a revised offer earlier this month. It was not accepted by the unions.

Prentis said the national strike on November 30 would be at least as big as a national strike during the Winter of Discontent in 1979 that helped Conservative leader Margaret Thatcher sweep to power.

Numbers might even match the 1926 General Strike when an estimated 3 million were involved, he said.

This is a momentous day, far bigger than people realise. When people write history books about politics in this country they will always refer to 30th November 2011, he said, adding that 9,000 employers would be affected, including some in the private sector, as many public-sector jobs had been privatised.

Prentis said more than 1,000 demonstrations had been planned across the UK by the Trades Union Congress (TUC) which was coordinating the stoppage. This is not just about picket lines around buildings, this is about people demonstrating showing the coalition what they are worth, he said.

TUC head Brendan Barber said it was unlikely there was anything the government could say to persuade unions to call off the strike.

Education Secretary Michael Gove said union chiefs were itching for a fight and that a militant faction wanted to inconvenience millions of hard-pressed families.

(Reporting by Stefano Ambrogi; editing by David Stamp)