PUBLIC services face disruption today as thousands of civil ­servants join as many as an ­one million workers south of the Border in a strike over pay.

Picket lines are due to be set up outside courts, government ­buildings including the Scottish Parliament, the National Museum and the National ­Galleries in ­Edinburgh as well as the Passport Office in Glasgow.

There will also be rallies in both cities.

The UK-wide action, estimated to be the biggest since the General Strike of 1926, will in England, Wales and Northern Ireland also involve teachers, firefighters, local government and transport workers. It is mainly about pay, which in the public sector was frozen in 2010 and has been capped at a 1 per cent rise since 2012.

At Westminster, the planned strike action was condemned by Prime Minister David Cameron, who told MPs the "time had come" to introduce thresholds on strike ballots; business leaders have been pressing for one at 50 per cent.

Labour's Ed Miliband also condemned the strike but made clear he would not condemn the strikers as this would only "ramp up the rhetoric" when what was needed were negotiations to resolve the issues.

The Public and Commercial Services (PCS) union said it was ­expecting a "strong response" from its 28,000-strong civil service membership in Scotland.

The industrial action, it stressed, was meant to send a clear message to both the UK and Scottish governments that public-sector workers had had enough of pay cuts.

The PCS said it was calling on Scottish ministers to break with the imposed UK austerity pay cap on its own workforce in the run-up to the September referendum.

"John Swinney doesn't need to wait for the referendum to break away from George Osborne and the pay policy of the Tories," declared Lynn Henderson, the PCS's Scottish Secretary.

"At any point in the last seven years he could have rejected a below-inflation pay cap and accepted the arguments of PCS that investment in public services, in public sector jobs, in fair pay for civil servants would help ­Scotland's economy and help the way out of recession."

Ms Henderson said that, instead, Scottish workers ­delivering government priorities had had a real-terms 20% pay cut, losing thousands of pounds as their pay was either frozen or capped.

"Our members will not sit back and watch public services being bled by austerity cuts. We will fight for jobs, decent pay, fair pensions and for properly funded public services for the people of Scotland," she added.

However, the SNP stressed how many Scottish public sector workers such as police officers, teachers, nurses, prison officers and those working within the ­Scottish Government had benefited from pay decisions made in Scotland and, consequently, received higher pay.

Stewart Hosie, the party's economics spokesman, pointed to the September referendum, saying: "There is an alternative for public sector workers than sticking with Westminster.

"A vote for independence is an opportunity to choose ­prosperity over austerity and a better way forward for the public sector."

The biggest disruption will occur south of the Border as ­thousands of workers from refuse collectors and cleaners to teachers and firefighters go on a one-day strike.

Picket lines will be set up outside the Houses of Parliament, courts, job centres, libraries, ­museums, town halls and council offices.

A major rally is also planned for Trafalgar Square.