No confidence vote: What happens if Boris Johnson wins or loses tonight?

Watch: Tory MPs trigger Boris Johnson vote of confidence

Boris Johnson is facing a vote of no confidence after at least 15% of Conservative MPs withdrew their support for the prime minister.

Sir Graham Brady, the chairman of the backbench 1922 Committee, announced on Monday that a vote had been triggered and will take place this evening between 6pm and 8pm, with the result expected at 9pm.

Johnson's political future hangs in the balance as, even if he wins tonight's confidence vote, his days could be numbered as Conservative leader and prime minister.

Why has the no-confidence vote been triggered?

The prime minister has been teetering on the edge for a number of weeks after being unable to shake the Partygate scandal.

A string of his own MPs had already called for him to stand down in the wake of Sue Gray’s report into breaches of the COVID-19 regulations in No 10 and Whitehall.

Read more: Boris Johnson suggests he considered quitting over Partygate

Johnson was fined £50 in April for attending his own birthday party in June 2020 with Gray's report, published last month, revealing a drunken culture in Downing Street.

The prime minister said he took "full responsibility for everything that took place on my watch" but said he wanted to "keep moving forward".

However, that was insufficient to sway enough Conservative MPs, who are worried they face heavy defeat in two upcoming by-elections later this month.

Voters in the constituencies of Tiverton and Honiton in Devon and Wakefield in West Yorkshire go to the polls on 23 June.

A survey by JL Partners reported in the Sunday Times predicted a 20-point lead for Labour over the Conservatives in Wakefield, which could signal that the Conservatives are beginning to lose the 'Red Wall' support that proved so crucial in its election victory.

What happens if Boris Johnson wins?

At least 50% – or 180 of the 359 Tory MPs – must vote against Johnson on Monday night for him to be ousted as prime minister.

Should he lose, there would be a leadership contest and he would be barred from standing.

If he wins, the current rules mean Johnson would be immune from another no-confidence vote for a year.

Read more: How Conservative MPs can get rid of Boris Johnson

However, Brady there is a possibility that rule could be changed. "Technically, it's possible," he said on Monday.

Even if Johnson wins the confidence vote, his leadership could be severely undermined.

His predecessor, Theresa May, won a no-confidence vote in December 2018 by 200 to 117 votes, but stumbled on for just six more months without the support of more than a third of her party, before resigning.

Johnson would be expected to battle on even if he is victorious by a small margin, but the medium term implications on his leadership would likely be difficult to keep a bay.

Defeats in the two by-elections could also spark renewed pressure on him to go.

What happens if Boris Johnson loses?

If Johnson is voted out or forced to resign, a leadership contest to replace him as Conservative leader would take place – although he would likely to remain prime minister until a successor is in place.

The contest takes place in two stages and would probably last for anything between six and eight weeks.

In the first stage, Conservative MPs put themselves forward as candidates.

All Tory MPs then vote in a series of rounds to reduce the number of candidates until only two remain.

The second stage of the contest sees the two remaining candidates put to a vote of Conservative Party members.

Johnson won the leadership contest in 2019 against Jeremy Hunt, following May’s resignation.

Who could be the next Tory leader if he loses?

Several members of Johnson's cabinet offered their support for the prime minister on Monday, all knowing that they are among the contenders to succeed him should he lose tonight's vote.

The most recent Tory leadership poll by the Conservative Home website showed that foreign secretary Liz Truss would be the most popular successor to Johnson among party members, followed by chancellor Rishi Sunak and trade minister Penny Mordaunt. Mordaunt was one of only a few senior MPs not to tweet a message of support for Johnson on Monday morning.

Health secretary Sajid Javid and home secretary Priti Patel are also likely to be in the frame for the leadership should Johnson be ousted.

Watch: Labour leader says Tory MPs should remove Boris Johnson