Liz Truss kickstarts leadership race after ending chaotic 45 days as PM

At a lectern outside Downing Street during another tumultuous day, Truss admitted that she could not deliver the radical economic mandate on which she was elected by Conservative members.

She will be the shortest-serving UK prime minister ever, having presided over what has been one of the most politically turbulent and economically damaging periods in modern history.

Keir Starmer, the Labour leader, led calls for an immediate general election, arguing it was untenable for the Conservatives to appoint yet another premier without a fresh mandate. Instead, Tory grandees set a deadline of Friday 28 October for the new contest to be completed.

The rivals to succeed Truss immediately embarked on urgent campaigns to sign up at least 100 Tory MPs by Monday afternoon to get on the ballot paper, with Sunak quickly gathering momentum to become the early frontrunner.

Johnson was said by MPs to be considering another tilt at the job, despite quitting in disgrace in July following a series of scandals that left his personal integrity in tatters. Friends said he was planning to return early from a Caribbean holiday to gather support.

Tory insiders claimed that, although popular with party members, Johnson was a deeply divisive figure among MPs and would struggle to reach the required threshold for nominations.

Penny Mordaunt, the leader of the Commons who came third last time round, could also make the first cut unless the right of the party backs one of their own instead. If only one candidate reaches the 100-MP threshold on Monday, then they will automatically take over.