THE UK Government is set to mount a legal bid at the UK Supreme Court in the next 48 hours, in an attempt to stop alternative Brexit Bills in Scotland and Wales from becoming law.

The unprecedented move, which could spark a constitutional crisis, would see Holyrood's Continuity Bill – and its equivalent in Wales – facing a legal challenge from the UK.

UPDATE: UK Government mounts unprecedented legal bid against Scotland's Brexit Bill

If agreement cannot be found on the UK Government's EU Withdrawal Bill, the continuity legislation would see powers in devolved areas returning to the UK post-Brexit remain with the devolved parliaments.

There are 111 powers and responsibilities in devolved areas due to be repatriated, but despite intense negotiations, there remains no consensus on 25 of those.

First Minister Nicola Sturgeon has refused to budge, refusing the UK's power grab, while Theresa May and her Government have argued that those policy areas must operate UK-wide to protect its internal market.

The Scottish Government believe they should be asked to agree any changes in those 25 areas, whereas the UK only wish to "consult" Scotland.

Theresa May's legal team have until Wednesday to launch the legal challenge, or the Continuity Bill will become law.

Attorney General Jeremy Wright and the Advocate General, Lord Keen of Elie, Whitehall's senior Scottish lawyer are expected to make the court application before then.

Scotland Secretary David Mundell earlier this week argued that the "almost inevitable" legal challenge was not a big deal, and simply a "process thing".

The UK has until May 8 to strike a deal with the devolved nations, but the Bill's parliamentary passage could be blocked before then in the House of Lords.

If the UK Government's Supreme Court legal challenge against Holyrood were then to fail, it would mean the Continuity Bills becoming law and control of the post-Brexit powers going to the devolved parliaments.