While Boris Johnson will announce his resignation, it is possible that he will remain in office until October, when the Conservative party meets for its annual conference.
Conventionally, when a Conservative leader resigns, they give the party time to hold a thorough leadership contest.
It is hard to predict how long this contest will take. When former Prime Minister David Cameron resigned in 2016, the process lasted just a few weeks as candidate after candidate pulled out, leaving Theresa May unopposed.
When Johnson himself ran in 2019, he went through several rounds of voting with his MPs, before being put to a final-two with the party membership. He defeated the former health secretary Jeremy Hunt in the final round. Hunt is expected to run for the leadership again.
While Johnson’s plan might be to stay on, given the near-collapse of his government, it is also possible that his MPs will demand an alternative interim leader.