A ruling on the legality of British Prime Minister Boris Johnson's decision to suspend parliament for five weeks will be announced by the UK Supreme Court at 10.30am tomorrow.
A panel of 11 Supreme Court justices will announce their findings following a historic hearing in London last week.
The judges have been asked to rule on whether Mr Johnson's advice to Queen Elizabeth to prorogue parliament until 14 October was unlawful.
Mr Johnson is in New York where he is to meet US President Donald Trump at the United Nations General Assembly tomorrow, where he will also meet key European Union leaders.
The Supreme Court judges, led by its president Lady Hale, heard appeals over three days from 17 September arising out of legal challenges in England and Scotland, which produced different outcomes.
At the High Court in London, Lord Chief Justice Lord Burnett and two other judges rejected a challenge against the Prime Minister's prorogation move by campaigner and businesswoman Gina Miller.
But in Scotland, a cross-party group of MPs and peers won a ruling from the Inner House of the Court of Session that Mr Johnson's prorogation decision was unlawful because it was "motivated by the improper purpose of stymieing Parliament".
Ms Miller's barrister Lord Pannick QC, told the Supreme Court that Mr Johnson's motive for an "exceptionally long" prorogation was to "silence" parliament, and that his decision was an "unlawful abuse of power".
But James Eadie QC argued on the prime minister's behalf that the suggestion the prorogation was intended to "stymie" parliament ahead of Brexit was "untenable".
Mr Johnson advised Queen Elizabeth on 28 August to prorogue parliament for five weeks and it was suspended on 9 September.
Mr Johnson claimed the five-week suspension was to allow the Government to set out a new legislative agenda in a Queen's Speech when MPs return to parliament on 14 October.
But those who brought the legal challenges argued the prorogation was designed to prevent parliamentary scrutiny of the UK's impending exit from the EU on 31 October.
At the close of the unprecedented proceedings, Lady Hale said: "I must repeat that this case is not about when and on what terms the United Kingdom leaves the European Union.
"The result of this case will not determine that.
"We are solely concerned with the lawfulness of the prime minister's decision to advise Her Majesty to prorogue parliament on the dates in question."