Fears in Europe that party’s goal of unseating PM could lead to chaos of ‘cliff-edge’ exit

The EU is intensifying its preparations for a no-deal Brexit amid heightened fears in European capitals that Jeremy Corbyn will order his MPs to vote down any deal struck in Brussels, a leaked document reveals.

Labour’s stated goal to reject Theresa May’s deal in order to spark a general election has provoked a rush of activity in Brussels, where the party’s plans are regarded as one of the substantial risks to the negotiations.

Shortly after Corbyn ended his leader’s speech at the Labour party conference, one of the European commission’s most senior officials addressed EU ambassadors on contingency planning in the event of a breakdown in talks, or a failure of the UK parliament to ratify an agreement struck in Brussels.

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A “restricted” document circulated among ambassadors in Brussels before Wednesday’s confidential meeting, warned of the prospect of Labour combining with rebel Tory MPs to kill off a deal.

The document, seen by The Guardian, said: “Preparedness work has to intensify in the months ahead at national as well as EU level, as uncertainty remains about the outcome of the negotiations and the ratification of a possible deal.”

The shadow business secretary, Rebecca Long-Bailey, said on Wednesday that it would take a miracle for Labour to support a deal brought back by May. One of the party’s six tests of any deal is that it offers exactly same benefits as the arrangements of today.

Corbyn echoed that warning in his leader’s speech, stating that Labour would vote down a plan that did not include a customs union with the EU, avoided a hard border on the island of Ireland and protected “jobs, people’s rights at work and environmental and consumer standards”.

The Labour leader is now expected in Brussels on Thursday to meet the EU’s chief negotiator, Michel Barnier, to explain his position. But there is growing concern that Labour’s determination to unseat May could instead propel UK into a “cliff-edge” Brexit, throwing the continent into chaos.

While Labour has insisted it will force a general election it does not in reality have the power to do so. The prime minister has insisted that she will present a binary choice to parliament of her deal or crashing out of the EU.

Before the meeting, Corbyn said: “With just weeks of negotiating time left, it’s clear that UK-EU Brexit talks are in a perilous state … Crashing out of Europe with no deal risks being a national disaster.”

He said he planned to urge EU officials “to do all they can to avoid a ‘no-deal’ outcome, which would be so damaging to jobs and living standards in both the UK and EU countries.”

On Tuesday Barnier, gave a downbeat analysis of the state of the negotiations during a private meeting with MEPs.

Afterwards, the leader of the Greens in the European parliament, Philippe Lamberts, told the Guardian: “I have zero trust in Labour, I am afraid to say. The Labour position is not to do with principles, but about tactical considerations. It is all about getting the government out of power whatever the cost.”

According to the leaked document the reality of a no-deal Brexit has also prompted the EU’s member states to go over the head of the European commission and assert their right to take a “political choices” on potential mini-deals with the UK to avoid the worst repercussions of such a scenario, including the grounding of flights between Britain and the EU.

The document says: “Contingency measures can only be triggered at a certain stage, and some political choices, eg as regards to the extent to which these measures should mitigate the effect of a disorderly withdrawal, will have to be made before the commission can provide possible answers.”

Earlier this month, Barnier reprimanded the Brexit secretary, Dominic Raab, after it emerged that the UK government had written to EU capitals to seek bilateral deals on transport, including aviation and haulage.

France’s finance minister, Bruno Le Maire, has claimed the EU has higher considerations than the UK’s economic health to deal with and it would be “suicidal” for the bloc to soften its stance in relation to May’s Chequers proposals for the future relationship.

“I’m sorry to say it so callously: there is something more important for us than the future of the UK, and that’s the future of the EU,” he said. “Any decision that would give European citizens the feeling you can exit the EU and keep all the advantages would be suicidal, and we won’t make that decision.”

An October summit, described by European council president, Donald Tusk, as the “moment of truth” in the Brexit negotiations is to be extended by an extra day to give leaders the maximum opportunity to analyse the situation.

The EU has insisted that progress must be sufficient on the contentious issue of avoiding a border on the island of Ireland, or a final Brexit summit pencilled in for mid-November to finish off a deal on the principles of the future relationship will be cancelled.