Labour leader Jeremy Corbyn will on Tuesday attempt to bridge deep divisions with other opposition parties on how to avoid Britain crashing out of the EU on October 31.
Corbyn said he would "do everything necessary" to stop a no-deal Brexit, following leaked official warnings that this could lead to food, fuel and medicine shortages.
The Labour leader has said he plans to call a no-confidence vote in Prime Minister Boris Johnson next week and if he wins it would be ready to lead a caretaker government.
But other opposition MPs favour passing a law that would force the government to ask the EU to delay Brexit.
Ahead of the talks, Corbyn wrote in the Independent that Johnson was "cosying up to" US President Donald Trump in the hope of securing a free trade deal after Brexit.
"A No Deal Brexit is really a Trump Deal Brexit," he said.
"It won't return sovereignty, it will put us at the mercy of Trump and the big US corporations," Corbyn wrote.
"I hope we can come to a good working arrangement and bring on board others across parliament who see the danger of a No Deal crash out," he said.
Speaking to BBC radio, Liberal Democrat leader Jo Swinson said she would be willing to discuss all possible options "because we do not have a lot of time".
Britain's parliament is not due to resume until next week.
But anti-Brexit politicians have been discussing plans ever since Johnson came to power last month vowing to take Britain out of the EU on October 31 with or without a divorce deal with Brussels.
Johnson has said he is hoping for a deal with EU leaders, describing the chances as "marginally" higher following G7 talks over the weekend.
But Johnson has not ruled out suspending parliament in order to allow a no-deal Brexit if he fails to come to an agreement with the EU in the next weeks.
Labour's Brexit spokesman Keir Starmer has said suspending parliament -- known as "proroguing" -- would be "unlawful" and "completely unacceptable".
The political impasse has raised the chances of a general election and politicians of all stripes are preparing.
The Brexit Party, which came first in European elections earlier this year and which advocates a no-deal Brexit, is presenting its candidates at a launch event on Tuesday.
Britain voted to leave the European Union in a 2016 referendum but has already been forced to delay its exit twice after parliament opposed a deal struck with Brussels under Johnson's predecessor Theresa May.
"Jeremy Corbyn's Labour Party will do anything to try and block delivering the change that British people voted for in the referendum," the Conservatives said in a statement.
"Only Boris Johnson and the Conservatives can provide the leadership the UK needs to deliver Brexit by 31 October, whatever the circumstances," the statement said.
