The lawyer representing the government has said the Prime Minister would “take the necessary steps” to comply with the Supreme Court if it rules that he suspended Parliament unlawfully.
But in that event, the Advocate General for Scotland, Lord Keen QC, did not rule out the possibility of Boris Johnson advising the Queen to prorogue Parliament for a second time.
Britain’s highest court was hearing appeals in two separate challenges to rulings over Mr Johnson’s controversial suspension of Parliament.
The government was appealing a Scottish court ruling that said sending MPs home was “unlawful”.
Lord Keen told one of the 11 judges, Lord Kerr: "If the court finds [prorogation] was unlawful, the Prime Minister will take the necessary steps to comply with any declaration made by the court."
He argued that the government suspended Parliament to allow a Queen’s speech for outlining new government policy.
The lawyer also insisted that MPs had the power to prevent or reduce their removal from the House of Commons, and therefore it should not be resolved by the courts.
Meanwhile, campaigner Gina Miller was at the court to challenge a dismissal of an earlier legal challenge on the issue.
A High Court in London had ruled that length of the prorogation was "purely political" and not a matter for the courts.
Mrs Miller's barrister, Lord Pannick QC, told the judges: "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."
Protesters on both sides of the Brexit debate assembled outside of the court in London, with signs reading “defend democracy” countered by cries of “we voted Brexit”.
The case will continue over the next few days.