After two hours of voting in Committee Room 14 in the House of Commons, Graham Brady, chairman of the 1922 Committee of Conservative backbenchers, said 200 Conservative lawmakers had voted in support of May as leader, and 117 against, indicating her party was bitterly divided over the direction of Brexit.
She added: "I think markets are most concerned that the United Kingdom could leave on March 29 without a deal in place, which many people think would be damaging for the economy and when we get that sort of muse then the pound suffers".
"That might include an addendum to the Withdrawal Agreement that sets out that Parliament will vote prior to going into a backstop, should that prove necessary, and potentially that the EU Parliament and UK Parliament must vote every year thereafter to provide that legitimacy for the UK to stay in the backstop, should that prove necessary", she told BBC Radio 4's Today programme.
The leadership challenge marks a violent eruption of the Conservative Party's decades-long divide over Europe and throws Britain's already rocky path out of the European Union, which it is due to leave on March 29, into further chaos. The EU has insisted the deal on the table is its best and final offer, and if negotiations reopen then it may reconsider some of its previous concessions.
The votes will be counted immediately afterwards and an announcement made on Wednesday evening.
Asked if she had been informed the 48-letter requirement was met, the prime minister said: "No, I have been here in Europe dealing with the issue I have promised Parliament I would be dealing with".
"Being PM (is the) most hard job imaginable right now and the last thing the country needs is a damaging and long leadership contest".
He said that if May lost, "I don't think we will be leaving the European Union on the 29th of March". The victor of the vote becomes Conservative leader and prime minister, without the need for a national election.
She warned that ousting her now, sparking a weeks-long leadership contest, would "create uncertainty when we can least afford it".
However, some lawmakers who have backed May publicly have said in private that they will vote against her, according to British political commentators.
Chief of staff favorite says no
Whipple noted that James Baker, who served as chief of staff to Presidents Ronald Reagan and George H.W. Trump is on pace to break that record, as he looks for his third chief of staff in less than 24 months.
"She said that in her heart she would like to fight the 2022 election, but that she recognised the party did not want her to, and therefore it was not her intention to", he said.
May received sympathy from European Union partners on her trip but firm rejections of any attempt to reopen the Brexit deal, which was only secured after 17 months of excruciating talks.
All 315 Tory legislators can vote on the confidence motion.
All Conservative MPs can vote.
The party membership would vote via a postal ballot on which of the two candidates should be party leader.
If British lawmakers approve the agreement, it must still be endorsed by European Parliament members before March 29.
As the prime minister arrived, her colleagues weren't quite sure of the result.
The British pound, which has lost 25 cents against the US dollar since the 2016 referendum, was down 0.5 percent at $1.2501, falling after a Sky news reporter said a vote of confidence in May's leadership was about to be triggered.
Jacob Rees-Mogg, who has led backbench calls for her to go, said: "Theresa May's plan would bring down the government if carried forward".