STRASBOURG, France (AP) — The risk of Britain leaving the European Union without a divorce deal remains "very real," European Commission chief Jean-Claude Juncker declared Wednesday as EU lawmakers debated the ramifications of a no-deal Brexit.

Speaking at the European Parliament in Strasbourg, France, Juncker, who met with British Prime Minister Boris Johnson on Monday, said a no-deal Brexit "might be the choice of the U.K., but it will never be ours."

After the debate, the European Parliament is set to adopt a resolution laying out its concerns about Britain's impending departure from the 28-nation bloc on Oct. 31. Johnson has been adamant the U.K. will leave the EU on that date with or without a withdrawal agreement.

The main sticking point over a Brexit deal is the Irish border backstop, which would require Britain to respect EU trade and customs rules in order to avoid a hard border between EU member Ireland and the U.K.'s Northern Ireland until a better solution is found.

"I have no sentimental attachment to the backstop," Juncker said, adding, however, that he remains attached to the purpose it serves, which is not to create border structures that could be detrimental to peace in Northern Ireland.

"That is why I called on British prime minister to come forward with concrete proposals, operational and in writing on all alternatives that would allow us to reach these objectives," Juncker said.

EU leaders have made clear that any amendment to the current proposed divorce deal should preserve the bloc's single market and uphold the Good Friday peace agreement that ended decades of conflict in Northern Ireland.

Despite his declaration that Britain will leave on Oct. 31 "do or die," Johnson insists he can strike a revised divorce deal with the bloc in time for an orderly departure. European leaders are skeptical of that declaration.

"I asked the British prime minister to specify the alternative arrangements that he could envisage," Juncker said. "As long as such proposals are not made, I cannot tell you — while looking you straight in the eye — that progress is being made."

The Brexit agreement made with the EU by Johnson's predecessor, Theresa May, was rejected three times by Britain's Parliament, prompting May to resign and the fiercely pro-Brexit Johnson to come to power in July.

Spelling out the need for the backstop, EU chief Brexit negotiator Michel Barnier warned that even if Britain leaves without any agreement at all, several major problems will still have to be resolved, including the future of citizens hit by Brexit, peace in Northern Ireland and the protection of the EU's single market and the Irish economy.

"None of these questions disappears," Barnier said Wednesday, insisting that the challenges must not be underestimated. "We need legally operative solutions in the withdrawal agreement to respond precisely to each problem — to address each risk — that Brexit creates."

"Some three years after the British referendum, it's not a question of pretending to negotiate. It's our responsibility to continue this process with determination and sincerity," Barnier told the European lawmakers.

In London, Britain's Supreme Court resumed its hearing to determine whether Johnson's decision to suspend Parliament was illegal. Judges must determine if Johnson overstepped his authority by suspending Parliament for a five-week period during the run-up to the Brexit deadline.

The government's opponents argue that Johnson illegally shut down Parliament just weeks before the scheduled Brexit date for the "improper purpose" of dodging lawmakers' legitimate scrutiny of his Brexit plans. They also say Johnson misled Queen Elizabeth II, whose approval was needed for the shutdown.

Speaking in Strasbourg, the European Parliament's top Brexit official attacked Johnson's decision to prorogue Parliament. Noting that Eurosceptic politicians often criticize the EU for being undemocratic, Guy Verhofstadt said EU leaders "can do a lot of things, but at least they cannot close the doors of our house. That is not possible."

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Samuel Petrequin reported from Brussels. Lorne Cooke in Brussels and Jill Lawless in London contributed.

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