(Reuters) – On Monday, Prime Minister Boris Johnson will be subject to a confidence vote after over 15% of the elected Conservative legislators withdrew support following “partygate”, the scandal that saw British leaders being accused of stealing their votes.

Johnson was a key player in the Conservatives winning a majority of seats in 2019. He has since apologised, but said that he will not resign following a damning report detailing illegal parties within his Downing Street office.

The following is a detailed explanation of how Johnson’s challenge to leadership will be handled under the Conservative Party rules.

How did the leadership problem arise?

If 15% of Conservative Members of Parliament (MPs), write letters asking for a confidence motion to the chairman, the “1922 Committee”, representing party members who aren’t employed by the government, a leadership challenge can be triggered.

There are 359 Conservative MPs. 54 letters were required.

The Chairman of 1922, Graham Brady, stated Monday that the threshold had been crossed and that a vote to confirm this was being held from 6-8 pm (1700-1900 GMT Monday).

What is the Confidence Vote?

Johnson will be able to vote with all 359 Conservative MPs. Johnson would get 180 votes.

It is unclear how much of Johnson’s revolt was revealed. While not all those who sent letters requested Johnson to be removed, around two-dozen others did so in writing.

Johnson has received support from senior cabinet members. According to the Institute for Government, 160-170 legislators hold some government positions. They would normally be expected to quit if they wanted to challenge government on an important issue. Although some lawmakers have resigned from government in protest of “partygate”, confidence votes are run secretly by Conservative legislators.

Johnson is in office for the next 12 months, regardless of whether he wins. Johnson must resign after he loses. He is also barred from the following leadership elections.

– What happens to Johnson if he wins the confidence votes?

Johnson might theoretically stay in his job for at least one year. But, it is possible to change that rule.

Brady was asked if the timeframe could be reduced. However, Brady stated that it was technically possible that rules might be modified, however, that at present there would be grace periods.

Johnson could lose his position as leader even if he is not subject to a second vote of confidence.

Johnson’s predecessor Theresa May was elected to her confidence vote by 200 votes to117 in December 2018. However, the pressure to quit continued when she failed to secure Britain’s exit from the European Union in time. She resigned less than six months after that.

Johnson could lose.

Johnson could lose and there would be a contest for the leadership. Johnson’s replacement would then become the prime minister.

To reduce the number of candidates, Conservative MPs hold a secret vote. One ballot is cast among Conservative lawmakers to elect the candidate who has received the most votes. This process continues until there are two remaining candidates. Votes typically take place on Thursdays or Tuesdays, and can be held for several days.

Next, the final two candidates will be put to the Conservative Party members via postal ballot. The winner is then named as the new leader. The voters must have been members of the party for at least three months.