NICOLA Sturgeon could use the threat of Holyrood passing its own Brexit bill to pressure Theresa May into making sought after changes to the UK Government’s own legislation, a leading academic has suggested.

Professor Sionaidh Douglas-Scott said the "greatest value" of a Scottish EU Continuity Bill could be "the political pressure it might exert on the UK Government to amend Clause 11" of its flagship EU Withdrawal Bill.

The Scottish Government still believes the UK legislation is not fit for purpose and that Clause 11, dealing with devolved powers, is a “power-grab”; a contention rejected by Whitehall.

Insisting that, as things stand, Holyrood should not give its consent to the Withdrawal Bill, Edinburgh says it will draw up its own Continuity Bill as early as next month to ensure that there is a legislative insurance policy in place to protect Scotland’s system of laws from the disruption of Brexit.

Michael Russell, the SNP administration’s Brexit Minister, and Joe Fitzpatrick, its Parliamentary Business Minister, have told Scottish parliamentary officials that the Continuity Bill did not mean that the Scottish Government had definitely resolved to reject the UK legislation.

But they said: "Unless and until the necessary changes to the bill are made, the Scottish Government must provide for an alternative so that, on any scenario, there is a legislative framework in place for protecting Scotland's system of laws from the disruption of UK withdrawal from the EU."

Much to the anger and dismay of opposition MPs and indeed Scottish Conservative ones, the UK Government failed to honour a commitment to amend the Withdrawal Bill in the Commons; it will now be amended in the Lords.

But peers have already raised the prospect of a constitutional crisis should Edinburgh and Cardiff fail to give their consent to the legislation, saying that in such circumstances the Lords could decline to pass the UK legislation.

Prof Douglas-Scott pointed out how the UK Government could initiate a legal challenge if MSPs passed a Continuity Bill; or it could simply decide to override it.

In a guest post on the Scottish Parliament Information Centre's new blog site, the expert, from the Queen Mary University of London, said: “Even if a Scottish Continuity Bill were upheld in the courts, it would still be open for the UK Government to enact the Withdrawal Bill for the whole of the UK.

"The UK, as a sovereign Parliament, may override legislation passed by devolved legislatures," she explained.

But Prof Douglas-Scott noted it would be a “grave matter politically to ignore a constitutional convention and so act unconstitutionally".

She went on: "Therein lies perhaps the real utility of a Continuity Bill: in pushing the UK Government into a situation where it must either permit devolved nations to retain control of retained EU law in devolved areas or explicitly override a Continuity Bill and/or the devolution settlements without their consent.

"At present, the greatest value of a Continuity Bill may be the political pressure it might exert on the UK Government to amend Clause 11 of the Withdrawal Bill and so make it possible to adopt it with the Scottish Parliament's consent."

Peers are due to begin their deliberations next week when the bill’s Second Reading is taken over two days. Mr Russell is due to address them in a private briefing the day before the bill begins its passage.

No 10 was asked why the Prime Minister was confident that both Holyrood and Cardiff Bay would consent to the Withdrawal Bill given their steadfast opposition to it thus far. A spokesman stressed this was an important piece of legislation, which was “in the interests of all parts of the UK” to ensure Brexit was as smooth as possible.