THERESA May is set to mount a legal bid at the UK Supreme Court in an attempt to stop Scotland's alternative Brexit Bill becoming law.

Holyrood's Continuity Bill, and its equivalent in Wales, would see powers in devolved areas returning to the UK post-Brexit kept with the devolved parliaments – if agreement cannot be found on the UK Government's EU Withdrawal Bill.

READ MORE: Mundell is wrong: challenging the Continuity Bill is a big deal

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

First Minister Nicola Sturgeon has refused to budge in refusing the UK's power grab, while Theresa May and her government have argued 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.

The Prime Minister's legal team have until Wednesday to launch their 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, could make the court application as early as Monday.

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

Without consent from Scotland and Wales on Westminster's EU Withdrawal Bill, a constitutional crisis could be sparked.

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.