LONDON/BRUSSELS — Opposition parties said they would try to pass a law which would force Prime Minister Boris Johnson to seek a delay to Britain’s departure from the European Union and prevent a potentially chaotic no-deal exit at the end of October.

The United Kingdom is heading toward a constitutional crisis at home and a showdown with the EU as Johnson has pledged to leave the bloc in 66 days without a deal unless Brussels agrees to renegotiate the Brexit divorce.

Parliament returns from its summer break next week and is preparing for a battle with Johnson, who has vowed to take Britain out of the European Union at the end of October with or without an exit agreement.

Labour Party leader Jeremy Corbyn hosted talks with opposition parties on Tuesday where they agreed that passing a law to force the government to seek a delay to Britain’s EU departure would probably have the most support.

"We are going to come together and do the right thing by our country," said Anna Soubry, leader of The Independent Group for Change party. "We are up against a prime minister who has no mandate for this and I think he has no regard for parliament."

The opposition parties are seeking to repeat what they did earlier this year when lawmakers seized control of the parliamentary agenda to pass a law forcing Johnson's predecessor Theresa May to seek an extension to Britain's EU membership.

They also managed to change legislation to require parliament to be sitting for several days in September and October, making it harder for Johnson to shut down parliament to pursue a no-deal, something he has not ruled out doing.

The pound hit its strongest since July 29 against the dollar and euro after the parties presented a united front on Tuesday.

Britain is on course for a no-deal exit on Oct. 31 unless parliament can stop it or a new deal is reached with the EU.

The British parliament has rejected three times the withdrawal deal agreed between the last government and the EU, deepening a three-year crisis that threatens Britain's status as one of the world's preeminent financial centers and a stable destination for foreign investors.

Johnson held talks last week with German Chancellor Angela Merkel, French President Emmanuel Macron and European Council President Donald Tusk about his demand that the Brexit deal on offer is changed to remove the so-called backstop, an insurance policy to prevent the return of a hard border in Ireland.

He is due to talk by phone with European Commission President Jean-Claude Juncker on Tuesday and earlier spoke to Dutch Prime Minister Mark Rutte. A UK official said Johnson's Brexit adviser David Frost would travel to Brussels on Wednesday for informal discussions.

EU officials say they are listening to Johnson's arguments to replace one of the most hotly contested elements of the divorce agreement, something the bloc has previously said it will not agree to. A British official said it was felt there had been a softening in the EU's rhetoric around the backstop.

"It's good that there is a vibrant discussion, ideas are put forward but it’s up to the UK government to come up with concrete proposals that would be compatible with the Withdrawal Agreement," European Commission spokeswoman Mina Andreeva said.

One EU diplomat said Johnson had not made any big mistakes at the G7 summit in France at the weekend, his first outing on the international stage since taking office last month.

"If we could get something similar and if this thing would not be called a backstop - we could have success. All this may mean that, in the end, Johnson will have proven himself to be a refined strategist rather than suicidal," the diplomat said.

Votes in parliament have shown there is majority support for measures to block or hinder a no-deal exit. But any majority would be unstable, made up of lawmakers from different parties that are ideologically opposed, except when it comes to stopping a disorderly Brexit.

Liberal Democrat leader Jo Swinson has previously said Corbyn should drop the idea of trying to become caretaker prime minister if parliament forces the government's collapse.

But the parties agreed if their attempt to change the law was unsuccessful, they would consider forcing the government's collapse in a no-confidence vote. — Reuters