PM Boris Johnson's suspension of parliament is before Britain's High Court, with the judges to deliver judgment the next day; the decision may be appealed.
British Prime Minister Boris Johnson abused his powers by suspending parliament from next week until shortly before Britain is due to leave the European Union, London's High Court has been told.
Mr Johnson announced at the end of August that he would suspend parliament from mid-September to mid-October, just before Britain is due to exit the EU on 31 October, so the government could announce a new legislative program.
In a judicial review of that decision, brought by campaigner Gina Miller who defeated the government over another Brexit issue two years ago, the High Court was told parliament had never been suspended for so long in the past 40 years.
Ms Miller's lawyer, David Pannick, said comments from the PM showed that an important part of his reasoning for the prorogation, or suspension, was that parliament might say or do something that impeded the government's Brexit plans.
He cited Johnson's note to aides on 16 August dismissing the September gathering in the House of Commons as a "rigmarole" and saying he did not see "anything especially shocking" about suspending parliament.
"It breaches the legal principle of parliamentary sovereignty," Mr Pannick said on Thursday.
"What the prime minister is not entitled to do is to close parliament for five weeks at such a critical time without justification."
Mr Johnson, who took office in July, has promised to take Britain out of the EU on 31 October with or without a withdrawal agreement.
The legal challenge has lost some of its impacts after MPs voted this week to force Johnson to seek a three-month delay to Brexit rather than leaving without an agreement at the end of October and there could soon be a general election.
James Eadie, the government lawyer, said the question of suspension was "inherently and fundamentally" political and not a matter for the courts.
He said Mr Pannick's central argument was that MPs would not be able to legislate over a no-deal Brexit but that events of the last days "indicate that that is just untenable" and rendered the proceedings "slightly pointless".
Ian Burnett, the Lord Chief Justice of England and Wales, said he and two other senior judges would aim to give their verdict at 9am local time (1800 AEST) on Friday.
The ruling is likely to be appealed to the Supreme Court, Britain's highest judicial body, which has pencilled in for17 September to hear the case.
On Wednesday, a Scottish court hearing a similar case ruled that Johnson's decision was not one for judges to decide. A similar legal challenge in Northern Ireland will also be heard on Friday.