NICOLA Sturgeon will today stage a Downing Street showdown with David Cameron, telling the Prime Minister that the Conservative Government’s imposition of tough new trade union reforms in Scotland is “unacceptable”.

The First Minister will use a meeting in No 10 - ostensibly about the fiscal framework on new powers for Holyrood and on counter-terrorism co-operation - to “take the fight” to Whitehall over what UK Government critics believe is an attempt to neutralise trade union power.

Last week for the first time, Ms Sturgeon shared a political stage with Labour leader Jeremy Corbyn at a STUC event in Glasgow. Both politicians spelt out their opposition to the Trade Union Bill, which the UK Government insists creates a fairer balance between the rights of workers and of ordinary citizens.

If passed, the legislation will introduce a threshold for strike ballots, new measures on picketing and will allow companies to hire agency staff to cover for strikers. It is due to be debated in the House of Lords in January.

Ahead of this afternoon’s meeting, the FM said: “There is clear opposition across Scottish society and across the Scottish Parliament to this damaging piece of legislation.

“The number of days lost to strike action have been reduced in Scotland by 84 per cent through partnership working, not by slapping sanctions on workers.”

She added: “To impose this bill on Scotland would be an unacceptable step and I will make that clear to the Prime Minister.”

The SNP Government and the Scottish Parliament believe that because certain aspects of the bill will impact on Scotland, then they should have the right to block its application north of the border.

But the UK Government insists the legislation is UK-wide and reserved to Westminster, and, in a blow to Ms Sturgeon and her colleagues, Tricia Marwick, the Scottish Parliament’s presiding officer, agreed.

After legal consultation, a proposed legislative consent memorandum to block the bill’s measures being implemented in Scotland was deemed “not competent”.

A Scottish Government spokeswoman said the SNP administration would be “seeking other ways for the Scottish Parliament to express discontent with the legislation”. As yet, it is not known what they are.

The PM/FM meeting will also examine progress, or the lack of it, on the framework, which seeks to set out the practical implementation of the new tax powers for Holyrood and, in particular, the gradual withdrawal of money from the annual block grant.

Ahead of the no 10 talks, Mr Cameron said: “Both the UK Government and the Scottish Government are committed to getting a good deal for Scotland and these discussions are continuing in good faith.

“What I am absolutely clear on is that we must abide by the Smith principles; that is the promise we have made to the people of Scotland. This means that the fiscal framework must be fair to Scotland, fair to the rest of the UK, and built to last.”

Ms Sturgeon echoed the concerns of economists, who have warned that if the financial mechanism is not calibrated correctly, then the Scottish Government in coming years could lose hundreds of millions of pounds a year in revenue.

“We need a fair deal for both governments; no more, no less,” declared the FM, saying the framework process was critical to Scotland’s economic future.

”The Smith Commission was clear that the Barnett Formula must continue unaltered and that the Scottish or UK Governments should be no better or worse off simply as a result of the transfer of powers; before any policy decisions are taken.

“It is absolutely crucial that future Scottish Governments can use the new tax and spending powers, to create a fairer society and grow the economy, without losing out.”

She added: “Today is not about agreeing a final deal but I hope we can make significant progress in agreeing that the deal must be a fair one.”

Also, the two leaders will discuss how there can be better intergovernmental co-operation on fighting the terrorist threat.

Mr Cameron insisted the threat from Islamic State or Daesh applied across the whole of the UK, so it was “essential the UK Government and the governments of our devolved nations co-operate in the most effective way…including the use of intelligence information and we also need to ensure co-operation at a legislative level as well”.