A ruling on the legality of Boris Johnson decision to suspend Parliament for five weeks will be announced by the Supreme Court on Tuesday at 10:30 BST.
The government argues prorogation is not a matter for the courts, but critics say the PM is trying to limit MPs’ scrutiny of his Brexit policy.
Parliament is currently due to return on 14 October, with the UK scheduled to leave the EU on 31 October.
The case is being considered by eleven justices of the Supreme Court.
During the court case, government lawyer Lord Keen QC said prorogation was “forbidden territory, which is a matter between the executive and Parliament”, and MPs “had the tools” to change the law if they did not like it.
However, Lord Pannick QC – the lawyer for campaigner Gina Miller, who is challenging the prorogation – argued it “was motivated, or at least strongly influenced” by Mr Johnson’s belief that Parliament was “a threat to the implementation of his policies”.