DAVID Cameron’s controversial trade union reforms are “crumbling”, the SNP has claimed, after a leaked UK Government letter suggested Whitehall was preparing to make significant concessions, including consulting with Scottish Government ministers.

Welcoming the shift, Labour demanded the Conservative government now scrap the “rotten” Trade Union Bill altogether.

The legislation, which would make it much harder for workers to strike and, Labour argues, will seriously cut its funding, has been met with fierce opposition north of the border from both unions and political parties. The Scottish Government has sought to oppose the legislation because it would impact on devolved services.

At the weekend, Scotland’s trade union movement was urged to fight "outside the law" in an attempt to kill the bill. Unite has called for all 630,000 union members in Scotland to resist the "malicious" legislation now going through in its final stages at Westminster.

A leaked letter from Nick Boles, the UK skills minister, has set out a series of concessions, including consulting the Scottish Government on the requirement for a 40 per cent support threshold for strike action in important public services, facility time - time spent on union activities - and check-off - arrangements for collecting union subs from salaries.

In addition, if this did not prove to be a sufficient safeguard, Mr Boles said he proposed disapplying the ban on check-off to devolved public services in Scotland and Wales.

The move has come about because it is believed the UK Government fears the House of Lords will defeat certain aspects of the bill. No 10 declined to comment, saying it did not comment on leaked documents.

The letter, leaked to the Socialist Worker as peers began debating the bill, also includes proposed concessions around issues such as the need for a picket supervisor to wear an armband, increasing the notice period for strikes from seven to 14 days and whether unions should be allowed to conduct e-ballots for strikes.

Chris Stephens for the SNP said: "This letter is further evidence that the Tories' draconian Trade Union bill is rapidly crumbling under pressure and this regressive legislation has no place in modern day Scotland.

"It shows that the Tories are desperately trying to make concessions and amendments in the face of defeats to this unnecessary and unwanted legislation.”

The Glasgow South West MP claimed the legislation, as it stood, would destroy industrial relations across the country.

"If the Tories are willing to exempt Scotland and Wales from certain provisions in the Bill, then they should also be prepared to scrap the whole thing completely," he added.

Angela Eagle for Labour said the leaked letter showed her party had been right to oppose the bill from day one and it was welcome that ministers now privately accepted large parts of it were not fit for purpose and would have significant legal and constitutional implications if it was forced through Parliament.

“The Trade Union bill is a divisive and partisan piece of legislation, which Labour opposes in its entirety and while the changes discussed in this leaked letter are important, they don’t go nearly far enough. The Tories should do the decent thing and scrap this rotten piece of legislation altogether,” said the Shadow Business Secretary.

Grahame Smith for the Scottish Trades Union Congress said the leaked letter was proof the Prime Minister had seriously over-stepped the mark on trade union rights and the principles of devolution.

"Our campaign to ensure that significant sections of the bill do not apply to devolved government is making serious inroads and we are grateful to all the Scottish political parties who have united with us in opposition to the bill.”

He argued that the clause on check-off should be disapplied across the UK not just in Scotland and Wales. But he admitted there was some relief that union members would continue to be entitled to pay their dues in the most straightforward way.

"However, the central elements of this nasty and ideological attack on our members' rights are still in this bill. We are, therefore, still committed to using every available means to defeat it," he added.

Lynn Henderson, Public and Commercial Services union national officer, echoed the point, saying while the concessions were welcome, the campaign to stop the legislation would continue.

"As the Bill is about to be scrutinised further by the House of Lords we will continue to put pressure on peers to oppose all aspects of the legislation," she said.