By Kylie MacLellan and Guy Faulconbridge
LONDON (Reuters) - Prime Minister Theresa May vowed to fight for her job in a leadership challenge on Wednesday triggered by Conservative lawmakers, saying a change could jeopardise Britain's divorce from the European Union.
Less than four months before the United Kingdom is due to leave on March 29, Brexit is in chaos with options ranging from a potentially disorderly no-deal departure to another referendum that could reverse it.
Speaking outside her Downing Street residence hours before the vote of confidence on her leadership, May said she would battle for her premiership with everything she had.
In a stark warning to Brexit-supporting opponents who instigated the challenge, May said if they toppled her then the EU exit would be delayed and perhaps even stopped.
A new leader would not have time to renegotiate a deal with the EU and secure parliamentary approval by the end of March, meaning the Article 50 withdrawal notice would have to be extended or rescinded, she said.
"A change of leadership in the Conservative Party now would put our country's future at risk and create uncertainty when we can least afford it," she said. "Weeks spent tearing ourselves apart will only create more division just as we should be standing together to serve our country."
A secret ballot will be held between 1800 and 2000 GMT on Wednesday in a room at the House of Commons, and an announcement made at 2100. Before the vote, May will speak to lawmakers at a closed meeting.
According to the rules, May could be toppled if a simple majority of Conservative lawmakers vote against her, though a significant rebellion could also undermine her position. At least 153 of her 315 Conservative lawmakers had expressed public support for her by 1255 GMT.
Brexit is Britain's most significant political and economic decision since World War Two, though pro-Europeans fear it will weaken the West as it grapples with the presidency of Donald Trump and growing assertiveness from Russia and China.
DEAL DEAD?
The outcome will shape Britain's $2.8 trillion economy, have far reaching consequences for the unity of the United Kingdom, and determine whether London can keep its place as one of the top two global financial centres.
The British pound rose to 1.2564.
May, a 62-year-old vicar's daughter who voted to remain in the EU, won the top job in the turmoil that followed the 2016 EU referendum but promised to implement Brexit, while keeping close ties to the bloc, as a way to heal a divided nation.
But on Monday she abruptly pulled a parliamentary vote on her deal - which seeks to keep Britain closely aligned with the EU after its exit - in the face of a probable rout.
Her trade minister, Liam Fox, said the government might not even put it to a vote unless the EU gave further reassurances on the so-called Irish backstop.
German Chancellor Angela Merkel said the 27 other members of the bloc would not change the Brexit deal the EU has spent two years negotiating.
Brexit-supporting lawmakers in her party say May has betrayed the people's vote in negotiations, while opponents say she struck a deal that is the worst of all worlds - out of the EU but with no say over many rules it has to abide by.
"Theresa May’s plan would bring down the government if carried forward," lawmakers Jacob Rees-Mogg and Steve Baker said in a statement.
"But our party will rightly not tolerate it. Conservatives must now answer whether they wish to draw ever closer to an election under Mrs May’s leadership. In the national interest, she must go."
PARTY DIVISIONS
A schism over Europe in the Conservative Party over Britain's relationship with the EU contributed to the fall of all three previous Conservative premiers - David Cameron, John Major and Margaret Thatcher.
Cameron bet all on a referendum he lost in 2016.
Now, May - whose personal standing was already weakened by a snap election last year which cost her a parliamentary majority - also sees her own fate at risk over Europe.
Senior ministers, including those for finance, foreign affairs, the environment and the interior, warned that changing leader at such an important moment in British history was folly.
But as investors and company bosses tried to gauge the ultimate outcome of the political crisis, some were betting that Brexit would be thwarted.
The EU's top court ruled on Monday that Britain could cancel its Article 50 notice to leave without permission from other members and without losing special privileges.
But if May's deal fails and Brexit is not delayed, then Britain could be heading towards a disorderly exit that investors fear will silt up the arteries of trade, dislocate supply chains and roil financial markets.
"We are working hard to make sure we get an orderly Brexit," Merkel, the EU's most powerful leader, said.