Theresa May facing party leadership challenge amid...

Conservative lawmakers in Britain will hold a vote of non-confidence on Prime Minister Theresa May's leadership that will see her removed as party and government leader if she loses.

Graham Brady, who heads a committee overseeing Conservative leadership contests, said he had received letters from at least 48 lawmakers asking for a vote.

As a result, he said, 'the threshold of 15 per cent of the parliamentary party seeking a vote of confidence in the leader of the Conservative Party has been exceeded.'

A secret ballot will be held between 6 p.m. and 8 p.m. local time on Wednesday evening (1 p.m. and 3 p.m. ET), with the results announced soon after.

The announcement throws Britain's already rocky path out of the European Union, which it is due to leave on March 29, into further chaos.

Speaking outside 10 Downing Street early Wednesday, May said she will 'contest that vote with everything I've got.'

May, who held many key roles in the party before becoming prime minister, said she has spent the past two years fighting for a Brexit deal that delivers for voters.

'And it is now within our grasp,' she said, pointing to her recent effort to gain support from leaders of the EU and nations like Germany.

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May cancelled a trip to Dublin to meet Irish Prime Minister Leo Varadkar, to stay in London and battle for lawmakers' support.

She said ousting her and holding a leadership vote — a process that could take weeks — could result in Brexit being delayed or even stopped.

'A change of leadership in the Conservative Party now will put our country's future at risk, and create uncertainty when we can least afford it,' she said.

Hard fight ahead

But many Tory lawmakers have been growing angry with May over her handling of Brexit, and the challenge comes days after she postponed a vote to approve a divorce deal with the EU to avoid all-but-certain defeat.

If she loses the confidence vote, May must step down and there will be a contest to choose a new leader. She will remain leader, and prime minister, until the successor is picked. But if she wins, she can't be challenged again for a year.

Pro-Brexit and anti-Brexit demonstrators shout at each other opposite the Houses of Parliament on Tuesday. (Henry Nicholls/Reuters)

Supporters of Brexit say May's deal fails to deliver on the clean break with the bloc that they want.

Pro-Brexit legislators Jacob Rees-Mogg and Steve Baker said in a joint statement that 'in the national interest, she must go.'

The chairman of the main opposition Labour Party added to the chorus of criticism on Wednesday, saying May's 'half-baked Brexit deal does not have the backing of her cabinet, her party, Parliament or the country.'

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'The Conservative Party's internal divisions are putting people's jobs and living standards at risk,' Ian Lavery said in a statement.

But Cabinet colleagues rallied to May's support.

Conservative MP Ed Vaizey told BBC News he thinks it's likely May will win. The move to challenge her leadership, he said, seems 'completely self-defeating.'

Home Secretary Sajid Javid tweeted that a leadership contest, with Brexit little more than three months away, 'will be seen as self-indulgent and wrong. PM has my full support and is best person to ensure we leave EU on 29 March.'