Boris Johnson suspended Parliament in order to “silence” MPs who he believed would try to disrupt his Brexit plans, the Supreme Court has been told.
Lawyers challenging the Prime Minister’s decision to “prorogue” Parliament for five weeks said there was "strong evidence" that he saw the Commons as "as an obstacle" to his plans to take the UK out of the EU on 31 October.
The move is being challenged in the highest court in the land after Scottish and English courts gave contradictory judgments on the issue earlier this month.
The Court of Session in Edinburgh found the move to have been “unlawful”, days after the High Court in London dismissed a challenge against it as a “political” issue that was not for the court to decide.
The Government has insisted that its decision to suspend Parliament until the Queen’s Speech on 14 October was so that ministers could introduce a fresh legislative agenda.
But Lord Pannick, on behalf of campaigner Gina Miller, who is appealing against the High Court ruling, said: "The exceptional length of the prorogation in this case is strong evidence that the Prime Minister’s motive was to silence Parliament for that period because he sees Parliament as an obstacle to the furtherance of his political aims."
The QC’s remarks came on the first day of the Supreme Court hearing, which is scheduled to last for up to three days and is being heard by 11 judges.
He added that it was "remarkable" that the PM had not made a witness statement explaining "why he decided to advise Her Majesty to prorogue Parliament for a period as long as five weeks and there is no evidence from the Cabinet Secretary or any other official explaining that".
He continued: “Parliament will be silenced for a substantial part of the period leading up to the deadline of 31 October, when issues of grave national importance are being addressed - or not addressed - by the Government...
"The evidence shows that the Prime Minister at best improperly regards Parliament as an irrelevance.”
Opening proceedings, Lady Hale, the president of the Supreme Court, said the judges faced “serious and difficult questions”, given that "three senior judges in Scotland have reached a different conclusion to three senior judges in England and Wales".
Lord Keen, acting on behalf of the Government, later argued against the claim that the progogation amounted to five weeks given Parliament would not have sat during the Autumn party conference period.
He said: "Although the planned prorogation will be 34 days, the expected conference recess of three weeks would mean that only one to three days would be lost in the week commencing 9 September and four in the week commencing 7 October.
"A total of seven days and yet later in his opinion he expresses his opinion about the extraordinary length of the prorogation on the basis that its five weeks rather than seven days.
"It was in reality seven sitting days that were going to be lost, not five weeks of sitting days.”
When asked what the practical reason was for losing seven days, he responded: "Why should it not be seven? Why should it one day, 14 days, how is the court going to judge what is an appropriate period for a prorogation determined by the executive in exercise of the royal prerogative?"
Lord Keen also told the court that the Government would take "all necessary steps to comply with any declaration" if the Prime Minister's decision was found to be unlawful in the final ruling.