Britain's governing Conservative Party has ordered a lightning-fast race that aims to have a new prime minister in place within a week at a time when UK can ill afford uncertainty at the top.
Boris Johnson and his former finance minister Rishi Sunak are leading potential contenders to replace British Prime Minister Liz Truss.
Candidates on Friday are canvassing support to become Conservative Party leader in a fast-tracked contest.
Truss quit on Thursday after six weeks in power. Those who want to replace her must secure 100 votes from Conservative lawmakers by Monday to run in a contest which the party hopes will reset its ailing fortunes.
With opinion polls suggesting the Conservatives would be all but wiped out if a national election were held now, the race is on to become the fifth British premiere in six years.
The winner will be announced on Monday or next Friday.
In what would be an extraordinary comeback, Johnson, who was ousted by his lawmakers in July but remains popular with party members, was being touted alongside Sunak as a likely candidate.
"He can turn it around again. And I'm sure my colleagues hear that message loud and clear," Conservative lawmaker Paul Bristow told LBC radio. "Boris Johnson can win the next general election."
But Johnson, who left office comparing himself to a Roman dictator twice brought into power to fight crises, might not reach the 100 vote threshold after his three-year premiership was blighted by scandals and allegations of misconduct.
READ MORE: Johnson comeback bid adds drama to UK political crisis
Great to see Secretary of State for Business @Jacob_Rees_Mogg committing to #BringBackBoris. 🗳— Bring Back Boris (@OnlyBorisCan) October 21, 2022
✅ Only Boris has a mandate from the public
✅ Only Boris has got the big calls right
✅ Only Boris can deliver on the promise to level up
✅ Only Boris can win the next election pic.twitter.com/MOYW4RhXUE
The Financial Times said a Boris comeback would be "farcical".
One of his former advisers, who no longer speaks to Johnson and requested not to be identified, said he was unlikely to reach the target, having alienated dozens of Conservative lawmakers.
Will Walden, who also once worked for Johnson, said the former leader was returning from holiday and taking soundings.
British defence minister Ben Wallace said he would not stand in the contest to replace Truss as prime minister and was leaning towards backing Johnson.
"At the moment, I would lean towards Boris Johnson," he told broadcasters, while noting that Johnson - who was forced from office just last month - still had "some questions to answer" over multiple scandals that tarred his three-year tenure.
Business minister Jacob Rees-Mogg tweeted his support, using the hashtag "#Borisorbust".
Sunak, the former Goldman Sachs analyst who became finance minister just as the Covid-19 pandemic arrived in Europe and was runner-up to Truss in the summer's leadership contest, is the favourite with bookmakers, followed by Johnson.
Third-placed is Penny Mordaunt, a former defence minister popular with party members who came third last time. None have formally declared their candidacy.
READ MORE: PM Truss resigns as UK political turmoil deepens amid new election demand