Scotland on Sunday understands there are grave reservations across Whitehall about the concessions being sought by the Scottish Government and the potential for them to be exploited by the party formerly led by Gerry Adams and Martin McGuinness.
Sturgeon and her Brexit minister, Michael Russell, are objecting to the UK government’s EU Withdrawal Bill arguing that it represents a power grab from Holyrood to Westminster.
On Tuesday, the dispute will come to a head when SNP and Labour MSPs combine to withhold Holyrood’s consent to the Bill – a move which will be seen as another step on the road towards a full-blown constitutional crisis.
With EU powers coming back to the UK, Scottish ministers are against the UK Government’s plans to retain temporary control over 24 policy areas in order to protect the UK internal market.
Instead of the powers in devolved areas such as farming and fishing coming straight to Holyrood, they would be temporarily frozen at Westminster so that UK-wide frameworks could be created on issues such as food labelling.
Theresa May and her ministers argue that such an approach is needed to prevent businesses being harmed by any divergence in regulations north and south of the border.
Sturgeon and Russell have argued that this approach will undermine devolution. They want the UK government to make further concessions by removing Clause 11 of the Bill, which transfers powers from Brussels to Westminster rather than Edinburgh.
Another option would be for the UK government to agree that any regulations preventing Holyrood from legislating in devolved matters for a temporary period of time must only be introduced when agreed by the Scottish Parliament.
But were the UK government to meet Sturgeon’s demands they would apply in all the devolved nations, including Northern Ireland. A UK government source said that this would hand a veto over UK frameworks not just to the SNP, but to Sinn Fein, should the power-sharing Northern Ireland Executive be restored.
Power-sharing would see Sinn Fein return to government as Northern Ireland’s largest nationalist party in partnership with the Democratic Unionist Party, the largest Unionist party, which also happens to be propping up the Conservatives at Westminster.
The DUP would be unlikely to countenance any sort of power deals that give its age-old rival any influence over UK policy. Sinn Fein, which believes in breaking up the UK to form a united Ireland, is still treated with deep suspicion by the UK political establishment.
Last night a UK government source said: “The EU Withdrawal Bill is about providing certainty. We have to be able to guarantee UK-wide frameworks in areas where they are required. That’s why we cannot go beyond the boundaries of the present devolution settlement and give devolved administrations a veto over UK-wide arrangements.
“We have to consider all scenarios. The veto would not just be in the hands of the SNP in Scotland or Labour in Wales but potentially Sinn Fein in a restored Northern Ireland Executive.
“It is not as simple as saying we should trust the Scottish Government.”
The SNP claimed the UK government’s attitude towards the powers dispute was “deeply irresponsible”.
SNP MSP Ivan McKee said: “Tory excuses for their attempted Brexit power grab on the Scottish Parliament are becoming increasingly desperate – and in this case deeply irresponsible. The solution to the power grab lies in the UK government treating Holyrood with respect – not in smears, fear-mongering, or dangerous attempts to use the very delicate situation in Northern Ireland to score political points. That can only make things worse for everyone.
“The Tories are being propped up by the DUP at Westminster and it would be outrageous if that deal was being used in any way to undermine the powers of the Scottish Parliament.”