On the third day of the Brexit case, James Wolffe QC (pictured right) will refer to the Sewel Convention as enshrined in law, contrary to UK government lawyers who argue this is unnecessary and that Article 50 can be triggered by means of the Royal Prerogative.

The case is expected to finish on Thursday, with a ruling due in the new year.

The Advocate General for Scotland, Lord Keen of Elie QC (pictured right), told the court yesterday that the Scottish government’s case was “fatally undermined” by the fact it lacks powers over foreign affairs.

He added it was “perfectly clear” that the Royal Prerogative applies in Scotland and the other nations of the UK.

He said: “There appears to be clear legal authority for the proposition that there is no material distinction between the foreign affairs prerogative as between Scotland and England.”

He added: “All foreign relations and foreign affairs, in particular all our relationships with the EU, are not within the competence of the devolved legislators.

“There is no means by which you can suggest the exercise of the foreign affairs prerogative is in any way impinged or qualified by devolution legislation.”

The Attorney General for Northern Ireland and the Welsh government are also intervening in the case.