British Prime Minister Boris Johnson. Photo: VCG

UK Prime Minister Boris Johnson was flying home on Wednesday as determined as ever to push through Britain's departure from the European Union but facing reinvigorated opposition to his plans after the Supreme Court ruled he had unlawfully suspended parliament.

It is unclear exactly what will happen next in the tortuous Brexit process following the court's momentous decision, although Johnson can expect a tongue-lashing when parliament sits again on Wednesday morning.

Johnson has rejected calls from some political opponents to resign but opposition Labour Party leader Jeremy Corbyn said on Wednesday now was not the time for parliament to try and bring him down.

"Quite simply, our first priority is to prevent a no-deal exit from the EU on the 31st of October," Corbyn said in an interview on BBC Radio 4.

Johnson has insisted he will lead Britain out of the EU on that date with or without an exit agreement, but most members of parliament are equally determined to prevent a so-called "no-deal Brexit" scenario.

The House of Commons, where Johnson has no majority, reconvened 11:30 am Wednesday after the Supreme Court ruling Tuesday that his decision to suspend it for five weeks was unlawful and therefore null and void.

Before the suspension, parliament had passed a law requiring Johnson to ask the EU to push back the deadline if no exit deal was agreed by October 19. Corbyn said he and other opposition legislators would focus on ensuring that Johnson abided by that law.

Asked by reporters in New York on Tuesday how he planned to overcome that legal obstacle, Johnson simply ignored the question and insisted Brexit would take place on October 31 come what may.

Johnson has repeatedly said his preferred Brexit outcome would be to agree an exit deal with the EU's 27 other members before the deadline and that he was hopeful he would achieve that.

However, EU negotiators say he has made no new proposals capable of breaking the deadlock over the issue of how to manage the border between Ireland, an EU member, and Northern Ireland, which is part of the United Kingdom, after Brexit.

Against that backdrop, reactions to the Supreme Court's blistering ruling among British politicians showed that divisions were deeper than ever.

Jacob Rees-Mogg, the leader of the House of Commons and one of the most ardent advocates of Brexit, was reported by British newspapers to have said during a conference call with Johnson and other cabinet members on Tuesday that the Supreme Court had carried out a "constitutional coup."

Senior cabinet minister Michael Gove was more moderate in public on Wednesday morning, telling several media that the government would respect the court ruling even though it "respectfully disagreed" with some of the justices' reasoning.