Jeremy Corbyn has said Labour will "do everything necessary" to halt a no-deal Brexit.
Ahead of a meeting with senior MPs opposed to leaving the EU without an agreement in place, Mr Corbyn declared the country was heading for a crisis under Prime Minister Boris Johnson.
A no-deal exit from the EU would amount to a "bankers' Brexit" benefiting the rich, Mr Corbyn said.
Writing in the Independent, he said: "The battle to stop no-deal Brexit isn't a struggle between those who want to leave the EU and those who want continued membership.
"It's a battle of the many against the few who are hijacking the referendum result to shift even more power and wealth towards those at the top.
"That's why the Labour Party will do everything necessary to stop a no-deal bankers' Brexit.
"We want an injection of democracy so the people can decide our country's future.”
Mr Corbyn repeated his calls for a general election and said Labour would offer a referendum “with a credible Leave option as well as the option to Remain”.
The comments came as The Guardian reported legal advice prepared for the Labour leader by shadow attorney general Shami Chakrabarti claims Mr Johnson would be committing the "gravest abuse of power and attack on UK constitutional principle in living memory" if he shut down parliament to force through a no-deal Brexit.
Among those attending today’s cross-party talks is Liberal Democrat leader Jo Swinson.
On Monday, Ms Swinson called for Mr Corbyn to step aside if an emergency government of national unity is formed in the event of a vote of no confidence in Mr Johnson.
The newly elected Lib Dem leader said Mr Corbyn could not command support across the Commons to ultimately secure an Article 50 extension: particularly “key Conservative MPs” opposed to no-deal but who have rejected the idea of the veteran left-winger leading a caretaker government.
Green MP Caroline Lucas, meanwhile, tweeted ahead of the talks: "Boris Johnson's intentions are clear: suspending Parliament, a crash out Brexit and blaming MPs for the chaos.
"We will not be bullied. We will not surrender parliamentary sovereignty to the right wing cabal in Number 10.
"MPs must unite to stop this abuse of executive power."
As the opposition talks take place, the Daily Telegraph reported Mr Johnson will be sending his "Brexit sherpa" to Brussels in an attempt to get a deal done by the October 31 deadline.
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The paper reported "sherpa" David Frost will meet senior EU officials to discuss alternatives to Theresa May's withdrawal agreement, which was defeated three times in the Commons this year and ultimately led to her resignation as Prime Minister.
