The Act of Union forbids the UK Government from triggering Article 50 without getting approval from MSPs as well as MPs, the Supreme Court has heard.

The Scottish Government's top lawyer, lord advocate James Wolffe, made the argument in his closing remarks to the court on Thursday.

Mr Wolffe is arguing on the behalf of the devolved administration that the court should force Downing Street to seek the consent of not just MPs but MSPs before beginning the process of leaving the European Union.

The Scottish Government says leaving the European Union will change the legislative competence of Holyrood.

Since the Scottish Parliament's creation, the UK Government has sought the consent of MSPs before changing Holyrood's range of powers through the Sewel convention.

The First Minister has said beginning Brexit will "directly affect devolved interests and rights in Scotland" and therefore "the consent of the Scottish Parliament should be sought before Article 50 is triggered".

Mr Wolffe said: "My Lord Hodge asked me whether the power given to parliament in article 18 of the Treaty of Union was given to parliament exclusively.

"I do so exclusively to parliament and to those authorised by parliament.

"Against the background of the Claim of Right and the Bill of Rights it would have been extraordinary if power to change laws in use within the Kingdom of Scotland, which is the phrase in use in the Act and Treaty of Union, had been given to the Crown."

He added: "The question of who had authority with regards to Scots Law was a matter of significance to the framers of the Union legislation.

"I say it is not a matter simply of footnoting, to note the power to change the laws of Scotland where given to power and, of course, to those whom parliament has authorised and not to the Crown.

"I say that is consistent with the limiting law of constitutional law that sets bounds of the us prerogatives and preclude the United Kingdom government from asserting the power to make the significant changes to the laws of the land by virtue of the prerogative which they claim in this case".

The 307-year-old piece of legislation, which created the UK, states: "...all other laws in use within the Kingdom of Scotland do after the Union and notwithstanding thereof remain in the same force as before but alterable by the Parliament of Great Britain".

At his appearance before the court on Wednesday, some judges questioned the relevance of the Scottish Government's argument to central issue of the case.

Last month, the High Court ruled against Downing Street and told the UK Government it cannot trigger Article 50 without getting parliament's prior consent.

Downing Street appealed to the Supreme Court to overturn the earlier verdict.

The hearing will conclude on Thursday with a verdict expected to be published by the court next month.

Theresa May has promised to start the Brexit process before the end of March.

On Wednesday, MPs backed the government's timetable by 461 votes in favour and 89 against.

After the legal mechanism is triggered, the UK Government will have two years to agree to a deal with the European Union.