British Prime Minister Theresa May delayed a vote on a Brexit deal negotiated by her government – a decision that throws her plan to leave the European Union into chaos.

May admitted her agreement would have been defeated by a “significant margin” at Tuesday’s vote, but warned those calling for a second referendum on leaving the EU would risk “dividing the country again”.

“It is clear that while there is broad support for many of the key aspects of the deal, on one issue – the Northern Ireland backstop – there remains widespread and deep concern,” May said.

The prime minister said she would first ask the EU for more “reassurances” over the main bone of contention: a “backstop” to ensure no hard border on the island of Ireland, which her critics say means Britain could end up indefinitely subject to EU rules after it leaves.

Announcing the delay, May was laughed at by some lawmakers when she said there was broad support for the deal and that she had listened carefully to different views over it – the result of 18 months of tortuous negotiations.

‘No-deal’ scenario

Despite postponing the vote, the Conservative leader insisted her deal was the best compromise between continued membership of the European Union and a “no-deal” Brexit, which would see the UK crash out of the bloc without key agreements on trade and movement in place.

Nevertheless, May said she would meet EU leaders to express concerns shared by opponents of her deal while making preparations for a “no-deal” scenario. Britain is scheduled to leave the bloc on March 29.

Alan Wager, from the group UK in a Changing Europe, said despite May saying she would go back to Brussels “the deal cannot be substantially changed”.

“I think she’s going to buy time and bring back the deal in January with a bit less time from MPs to say we’ve got a better option. She’s saying to MPs, ‘look it’s this or nothing’,” Wager told Al Jazeera.

“I think we’re looking at a period of instability that’s going to go on beyond March now.”

May’s government and parliament at large are divided along a number of divergent views, ranging from those who feel her deal does not go far enough in separating from the EU and others who feel closer cooperation is possible.

Many others believe the United Kingdom should not leave the EU at all.

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‘May needs to go’

Opposite parliament, a small but raucous crowd of demonstrators spanning both sides of the Brexit divide gathered near Westminster’s College Green to make their feelings clear.

Amid competing five-metre high Union Jack and European Union flags, 54-year-old business owner Catherine Ginn said she was “disgusted” by Monday’s events.

“I think May has chickened out of this vote because it’s clear she’s not going to get it through. But I don’t care about this deal, the only deal I care about is remain,” Ginn told Al Jazeera.

Others, meanwhile, said the British prime minister had failed to deliver a definitive enough Brexit.

“May needs to go, she is well past her sell-by date and we need a new prime minister,” Tony Blighe, a 59-year-old retiree, told Al Jazeera.

“We need someone to stand up and say negotiations have failed and we are leaving on March 29 under World Trade Organisation rules,” he added.

No-confidence motion

Inside the Commons, May now faces the threat of a no-confidence motion.

If triggered and successful, it would end the rule of her government.

Opposition Labour party leader Jeremy Corbyn told parliament: “The prime minister is trying to buy herself one last chance to save this deal. If she doesn’t take on board the fundamental changes required, then she must make way for those who can.”

Earlier, the leader of the Scottish National Party, Nicola Sturgeon, said she will support Labour if it lodges a no-confidence motion on May’s rule.

The leader of the Liberal Democrats, Vince Cable, also said his party would support a motion of no-confidence if it is called.

“With the fiasco today, the government has really lost all authority. I and my colleagues will fully support the leader of the opposition if he now proceeds to a no-confidence vote as duty surely calls,” Cable said.

Prominent Conservative Brexit hardliner, Jacob Rees-Mogg, also called on May to either “govern or quit”.

Pound plunges

European Council President Donald Tusk said on Monday Brexit would be discussed at the council meeting on Thursday, including how to help the British government ratify the exit process, but that the Withdrawal Agreement was not up for renegotiation.

“We will not renegotiate the deal, including the backstop, but we are ready to discuss how to facilitate UK ratification. As time is running out, we will also discuss our preparedness for a no-deal scenario,” Tusk said on Twitter.

The pound, the main gauge of international investors’ confidence in the country’s economy, fell to a 20-month low of $1.25, down a sharp 1.7 percent on the day.

Investors are worried the political gridlock in Britain over how to leave the EU is increasing the likelihood of the country exiting the bloc without a deal on future relations.

That is a worst-case scenario, the Bank of England says, that could lead to the deepest recession in about a century and a further plunge in the pound.