SCOTLAND’S most senior law officer has been jeered by MSPs after refusing to answer questions about what would happen if the SNP’s alternative Brexit Bill fell apart.

The Lord Advocate James Wolffe QC said he had spent a long time “avoiding hypothetical questions” when asked about the Bill being struck down by the UK Supreme Court.

MSPs had been quizzing him about his decision to certify the SNP’s Brexit continuity Bill as within Holyrood’s powers, despite Presiding Officer Ken Macintosh saying it is not.

Ministers introduced the EU (Legal Continuity) (Scotland) Bill on Tuesday as part of contingency planning for a constitutional crisis over devolved powers and Brexit.

The Scottish Government wants all powers in devolved areas repatriated from Brussels to go direct to Holyrood, while the UK Government wants some to lie at Westminster, pending the creation of UK-wide “common frameworks”.

Theresa May repeated the UK’s position at Prime Minister’s Questions yesterday.

With the two sides in deadlock, the SNP Bill is intended to transfer EU law in devolved areas into Scots law at Brexit, leaving reserved matters to UK Brexit legislation.

Mr Macintosh said the Bill was ultra vires as it breached EU law by creating powers that can only be exercised after Brexit.

LibDem Tavish Scott asked what would happen if the Bill was passed and became the sole legislation covering devolved EU laws, but the UK Supreme Court then agreed with Mr Macintosh and struck it down as incompetent.

Mr Wolffe, the Scottish Government’s most senior legal adviser, replied: “I’ve spent a lot of time in my professional career avoiding hypothetical questions.

"The only question that needs to be addressed at this point, from my perspective, is whether or not this Bill is within the legislative competence of the parliament. I think it would be unwise for me to speculate about what might happen in an uncertain future.”

The remarks provoked a mix of laughter and jeers from MSPs.

Tory advocate Donald Cameron asked if Mr Wolffe agreed with Mr Macintosh’s statement that “the consistent approach to interpreting the powers of the Parliament has been that legislation cannot seek to exercise competence prior to that competence being transferred”.

After Mr Wolffe again said he did not think it would be “wise or appropriate for me to express a definitive view on a hypothetical question”, there was more jeering from MSPs.

Thereafter, MSPs frequently made ironic cries of “hypothetical” and “speculation”.

Tory Adam Tomkins said he agreed with Mr Macintosh that the key issue was not when the legislation would take effect, but whether it had legal validity in the here and now.

The Lord Advocate insisted the Bill had been “carefully framed” so as not to infringe EU law.

He said: “I would suggest that there is nothing in this Bill which is incompatible with EU law.”

Mr Scott said afterwards: “If the Supreme Court subsequently agrees with the Presiding Officer’s interpretation and strikes down the legislation it leaves Scotland as the only part of the UK without continuity legislation.

“We would have to beg the UK Parliament to take through a new piece of legislation.

“That would be the worst possible situation for people and businesses in Scotland.”

After the session, SNP Brexit Minister Michael Russell clapped Mr Wolffe on the shoulder.

The Scottish Government insists its preference was for the UK legislation to be amended to protect devolution, in which case the Scottish Brexit Bill would be abandoned.