Boris Johnson and Rishi Sunak have reportedly held late-night talks, fueling speculation they could reach a deal.
Neither the former prime minister nor the ex-chancellor have officially declared themselves in the running to succeed Liz Truss as prime minister.
The race to be PM heats up – follow the latest updates
Image: The expected timeline of events in the election of a new prime minister
To be included on the ballot, leadership candidates need the support of at least 100 Conservative MPs.
Public endorsements mean Sunak has passed that threshold, with 121 backers, and Johnson’s allies say he also has the numbers to run.
However, the latest Sky News count suggests just 56 MPs have confirmed they would back Johnson’s campaign to become prime minister for a second term.
One of Sunak’s supporters, Richard Holden, rejected claims that Mr Johnson had 100 MPs behind him and said that number of public endorsements had not been made “because they don’t exist”.
The only person to throw her hat in the ring, Commons leader Penny Mordaunt, has been backed by 23 of her peers.
The current contest has been accelerated following the resignation of Liz Truss as Prime Minister, with nominations for the ballot closing at 2pm tomorrow afternoon.
Read more: Who do Conservative MPs endorse to be the next Prime Minister? MPs who applauded Johnson’s departure now call for #BringBackBorisAnalysis: Johnson dominates the conversation, but a win won’t be easy
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0:52 “I can’t have a liar in parliament”
Reports suggest that talks between Mr Johnson and Mr Sunak focused on a possible joint ticket.
It comes after the former prime minister returned to the UK from his holiday in the Dominican Republic in economy class, with some fellow passengers booing him as he boarded.
If all three candidates receive 100 backers, there would be a vote by MPs, with the two winners proposed to the party membership.
A vote would then take place, meaning the new leader would be chosen on Friday.
In a significant moment for Team Sunak, Kemi Badenoch threw her support behind the former chancellor after a number of big names had turned to Mr Johnson.
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1:18 What would it take to force a general election?
While admitting he had been a member of the “Boris Johnson fan club”, he warned the Tories were not “running a popularity contest” and that the party “is not a vehicle for any individual’s personal ambitions “.
Writing in The Sunday Times, Ms Badenoch said of her decision to endorse Mr Sunak: “Like any work colleague, we had our differences, which I explained when we were competing in the same competition.
“Now it’s imperative that he let people know the decisions he made that he knew were absolutely right.”
He also talked about his focus on inflation and reducing “unnecessary and wasteful spending.”
Meanwhile, former foreign secretary Dominic Raab said it was “difficult to see” how Johnson could become prime minister again when he is “absorbed and distracted” by the problems surrounding the party.
Speaking to Sky News, Raab said he was “confident” Sunak would enter the Tory leadership race and was the “most prominent candidate” among the field.
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