Labour Party Leader Jeremy Corbyn | Leon Neal/Getty Images Corbyn: I will prevent no-deal Brexit, ax backstop UK opposition leader makes bold promises to a conference of European socialists.

LISBON — Labour leader Jeremy Corbyn said Friday he would ensure “there is no situation where we crash out with no deal” amid an escalating Brexit-fueled political crisis in Britain.

Corbyn, speaking at the congress of the Party of European Socialists, promised to renegotiate the Irish border backstop arrangement with the EU if given the chance.

He warned that Prime Minister Theresa May is now “reduced to threatening economic chaos” in the face of certain defeat in a House of Commons’ vote set for December 11, describing the coming week as “constitutionally unprecedented” to reporters in Lisbon.

Asked if he could guarantee there would be no Irish backstop in a Labour-negotiated Brexit deal, Corbyn told Euronews “there certainly wouldn’t be a backstop from which you can’t escape.”

May told the BBC Thursday it would be impossible to seal a Brexit deal without a backstop, a view the EU has consistently repeated since the backstop was negotiated as an insurance policy for Ireland in December 2017.

“The backstop is an integral part of the Withdrawal Agreement but the backstop would be an integral part of any Withdrawal Agreement and of any deal negotiated with the European Union,” May said.

Corbyn said that he would instead seek to agree a tailored customs union that “does give us the opportunity to have a say in it all.”

The EU regards that position as an example of “cherry-picking,” which it insists is not possible when it comes to the EU's single market and freedom of movement of workers within the single market.

Corbyn told the socialist congress that May's Brexit deal is doomed because “it’s a bad deal that will make most Britons worse off,” adding that “the prime minister has signed up to an agreement that has united all of the opposition parties.”

However, Corbyn declined to commit to submitting a vote of no confidence in the prime minister if MPs reject the deal.

Corbyn gave some of his strongest pro-EU statements to reporters outside the congress hall: “I campaigned to remain. I voted to remain,” he said.