Foreign Secretary Liz Truss is widely expected to beat former chancellor Rishi Sunak to become the new leader of the Conservative Party.
The announcement is scheduled for around 12.30pm, with the winner expected to make a speech before spending the rest of the day finalising their choices for Cabinet and wider ministerial roles and writing their first prime ministerial speech.
Boris Johnson and his successor will go to Balmoral, rather than Buckingham Palace, for the appointment of the new prime minister on Tuesday, in a break from tradition.
The Queen will receive Mr Johnson on Tuesday at her Aberdeenshire home, where he will formally tender his resignation, and this will be followed by an audience with the new Tory leader, where she or he will be invited to form a government.
11.45am – Former chancellor Rishi Sunak left his home in London earlier this morning ahead of the announcement.