British MPs have voted on Theresa May's divorce deal with the European Union, rejecting it by a majority of 230 in a massive blow for the prime minister's plan.

The 432-202 vote in the House of Commons was widely expected but still devastating for May, whose fragile leadership is now under siege.

Lawmakers finally got their chance to say yes or no to May's deal after more than two years of political upheaval – and said no.

It was the biggest defeat for a government in the House of Commons in more than a century.

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The defeat leaves May's position precarious.

Opposition Labour leader Jeremy Corbyn promptly called a vote of no confidence in May's government. The vote will be held at 7pm Wednesday local time (NZT 8am Thursday).



The vote means further turmoil for British politics only 10 weeks before the country is due to leave the EU on March 29. If the government loses, it will have 14 days to overturn the result or face a national election.

It is not clear if it will push the government toward an abrupt "no-deal" break with the EU, nudge it toward a softer departure, trigger a new election or pave the way for a second referendum that could reverse Britain's decision to leave.

Amid the uncertainty, some members of parliament from both government and opposition parties are exploring ways to use parliamentary procedures to wrest control of the Brexit process away from the government, so that lawmakers by majority vote could specify a new plan for Britain's EU exit.

FRANK AUGESTEIN/AP Britain's Prime Minister Theresa May has been fighting to get MPs to accept her Brexit deal.

But with no clear majority in parliament for any single alternate course, there is a growing chance that Britain may seek to postpone its departure date while politicians work on a new plan.

Although May lacks an overall majority, she looks likely to survive the vote unless lawmakers from her Conservative party rebel. Northern Ireland's Democratic Unionist Party, which props up May's government, said it would support her.

"The House has spoken and the government will listen," May said after the vote.

May, who leads a fragile Conservative minority government, has made delivering Brexit her main task since taking office in 2016 after the country's decision to leave the EU.

FRANK AUGESTEIN/AP Leavers hold up signs next to pro-European demonstrators protesting opposite the Houses of Parliament in London.

"This is the most significant vote that any of us will ever be part of in our political careers," she told lawmakers as debate ended.

"The time has now come for all of is in this House to make a decision, ... a decision that each of us will have to justify and live with for many years to come."

But the deal was doomed by deep opposition from both sides of the divide over UK's place in the bloc.

Pro-Brexit lawmakers said the deal would leave Britain bound indefinitely to EU rules, while pro-EU politicians favoured an even closer economic relationship with Europe.

The government and opposition parties ordered lawmakers to cancel all other plans to be on hand for the crucial vote. Labour legislator Tulip Siddiq delayed the scheduled caesarean birth of her son so she could attend, arriving in a wheelchair.

ITN Prime Minister Theresa May closes the debate to cheers from backbenchers, and thanks everyone who has contributed to the "historic" debate.

As lawmakers debated in the House of Commons chamber, outside there was a cacophony of chants, drums and music from rival bands of pro-EU and pro-Brexit protesters. One group waved blue-and-yellow EU flags, the other brandished 'Leave Means Leave' placards.

The Spanish government has warned that the deal British lawmakers rejected was "the best possible" and that reopening negotiations "would lead to a dangerous scenario".

Spain's socialist government said the deal the European Union and Britain's government struck "is the option that best defends the interests of both parties, as well as the rights of citizens and economic actors".

It added after Parliament voted against the deal that Britain departing on March 29 without a plan for its interactions with the EU post-Brexit "is an improbable and undesirable scenario, but one that can't be discarded".

FRANK AUGESTEIN/AP Two men wearing shirts and hats supporting US President Donald Trump join Leave demonstrators protesting outside the UK parliament.

May postponed a vote on the deal in December to avoid certain defeat, and there were few signs ahead of Tuesday's (Wednesday NZT) vote that sentiment had changed significantly since then.

The most contentious section of the deal is an insurance policy known as the "backstop" that is designed to prevent the reintroduction of border controls between the UK's Northern Ireland and EU member Ireland.

Assurances from EU leaders that the backstop is intended as a temporary measure of last resort completely failed to win over many British skeptics, and the EU is adamant that it will not renegotiate the 585-page withdrawal agreement.

Arlene Foster, who leads Northern Ireland's Democratic Unionist Party – May's parliamentary ally – said her party voted against the deal because of the backstop.

"We want the PM to go back to the EU and say 'the backstop must go,"' Foster said.

Parliament has given May until Monday to come up with a new proposal. So far, May has refused publicly to speculate on a possible "Plan B."

Some Conservatives expect her to seek further talks with EU leaders on changes before bringing a tweaked version of the bill back to parliament, even though EU leaders insist the agreement cannot be renegotiated.

AP Britain is due to leave the EU on March 29 under the current timeframe.

European Commission president Jean-Claude Juncker returned on Tuesday to Brussels to deal with Brexit issues arising from the vote, amid signals May might be heading back to EU headquarters on Wednesday.

An EU official, who asked not to be identified because of the developing situation, said that it was "important that he is available and working in Brussels during the coming hours."

May had argued that rejecting the agreement would lead either to a reversal of Brexit – overturning voters' decision in the 2016 referendum – or to Britain leaving the bloc without a deal.

Economists warn that an abrupt break from the EU could batter the British economy and bring chaotic scenes at borders, ports and airports.

Business groups had appealed for lawmakers to back the deal to provide certainty about the future.

Mike Hawes, chief executive of the Society of Motor Manufacturers and Traders, said parliamentarians "hold the future of the British automotive industry – and the hundreds and thousands of jobs it supports – in their hands."

"Brexit is already causing us damage in output, costs and jobs, but this does not compare with the catastrophic consequences of being cut adrift from our biggest trading partner overnight," he said.

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