Prime Minister Theresa May will face a confidence vote today between 6 and 8 p.m. local time (1 to 3 p.m. Eastern time). The result is expected no later than 9 p.m. London time. What is a confidence vote, how does it work, and what happens afterwards?

What is a confidence vote?

Under the UK’s parliamentary system, the ruling party’s leader es prime minister. If the leader loses his or her support, Conservative members of Parliament vote to express their confidence, or lack of confidence, in their leadership.

How does a confidence e to be held?

Under the rules of the UK’s Conservative Party, 15 percent of its members of Parliament trigger a confidence vote by sending letters to the 1922 Committee. mittee’s leader, Sir Graham Brady, informed Theresa May last night that at least 48 of the 315 eligible Conservatives in Parliament had submitted such a letter. Some, like Mark Francois, released those letters publicly. In a public statement this morning, May responded, “I will contest that vote with everything I’ve got.” Brady announced that MPs had both added, and revoked, letters of no confidence on the eve of the vote.

What caused this confidence vote?

Theresa May’s government has been imperiled for months. She called a snap election for June 2017, which resulted in her losing 13 seats and her party’s majority. May, who voted to remain in the European Union in 2016, regularly gave way to the EU during Brexit negotiations and hammered out a deal that crossed the “red lines” she set forth in her Lancaster House speech. Her Brexit deal would have left the UK implementing EU regulations without having any vote over their content, imposed a different regulatory regime on Northern Ireland that the rest of the UK, and potentially left the entire UK in the customs union with no unilateral way to leave.

Her critics had been split amongst themselves about how to respond. Jacob Rees-Mogg publicly announced on November 15 that he submitted “a formal letter of no confidence in the leader of the party.” Others believed that May is likely to survive, and the European Research Group should wait until her Brexit plan failed in Parliament to replace her.

The final straw came Monday, when May announced she was delaying Parliament’s “meaningful vote” on her Brexit deal, after tallies show she was likely to lose by as many as 200 votes.

What happens during a confidence vote?

All eligible MPs vote in a secret ballot, on paper ballots. The party leader survives by winning a bare majority. Theresa May will need the support of at least 158 Conservative MPs to remain party leader.

What if the prime minister wins a confidence vote?

The prime minister continues to serve as party leader. Under Conservative Party rules, another confidence vote cannot be held for at least a year.

What if the prime minister loses a confidence vote?

The party leader must step down and cannot take part in the ensuing leadership contest.

New candidates may be nominated to stand for Conservative Party leader with the backing of at last two Tory MPs. If only one candidate is nominated, that candidate wins. In the event that more than two candidates enter the leadership contest, multiple rounds of voting are held, with the lowest vote-getter eliminated each round.

When only two candidates remain, the broader membership of the Conservative Party then vote via postal ballots. The party rules state that “all the members of the Conservative party in good standing who have been members for not less than three months prior to the date of the announcement of the vote of confidence” may vote. This reform was adopted in 1998.

If the prime minister loses a confidence vote, does he/she immediately step down as leader?

Not necessarily. The prime minister may continue as a caretaker until the party chooses a new leader.

How long would a leadership contest take?

The 2005 leadership contest took three months. If May loses this vote, the leadership contest will likely take less time – in part because, under Article 50, the UK will leave the European Union on March 29, 2019.

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