Boris Johnson and Rishi Sunak held talks late into the night, Sky News understands.
Reports suggest Mr Johnson and Mr Sunak’s talks focused on a potential joint ticket.
The discussion has fuelled speculation the pair could strike a deal – though neither the former prime minister nor the ex-chancellor have officially declared themselves in the race to succeed Liz Truss.
Race to be PM heats up – follow the latest updates
To be included on the ballot paper, leadership candidates need support from at least 100 Conservative MPs.
Public endorsements mean Mr Sunak has surpassed this threshold – with 121 backers – and Mr Johnson’s allies claim he has the numbers required to run too.
However, the latest Sky News tally suggests just 56 MPs have confirmed they would support Mr Johnson’s campaign to be prime minister for the second time.
One of Mr Sunak’s supporters – Richard Holden – rejected claims that Mr Johnson had 100 MPs behind him, and said this number of public endorsements had not been made “because they don’t exist”.
But Northern Ireland Secretary Chris Heaton-Harris told Sky News’ Sophy Ridge that the former PM “definitely” had the numbers, and Johnson ally James Duddrige claimed he had held a meeting with MPs at 8am to “reach out to other camps”.
The only person who has thrown their hat into the ring, Commons Leader Penny Mordaunt, has received endorsements from 23 of her peers.
Theresa May’s de-facto deputy, Damian Green, is backing Ms Mordaunt, telling Sophy Ridge she is “in it to win it” and confident of reaching the nomination threshold.
And he warned against the race being “stitched up behind closed doors by big figures at Westminster” as party members “will feel cheated”.
The current contest has been expedited following Liz Truss’s resignation as prime minister, and nominations for the ballot paper are due to close at 2pm tomorrow afternoon.
Read more:
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Analysis: Johnson dominates talk, but a win won’t be easy
The talks come after Mr Johnson jetted back 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 were to receive 100 backers, there would be a vote by MPs – with the winning two put forward to the party membership.
A vote would then take place, meaning the new leader would be chosen by Friday.
In a significant moment for Team Sunak, Kemi Badenoch threw her support behind the former chancellor after a string of big names had flocked to Mr Johnson.
While she admitted that she had been a member of “the Boris Johnson fan club”, she warned the Tories are not “organising a popularity contest” – and the party is “not a vehicle for any one individual’s personal ambitions”.
The ex-PM’s campaign faced another blow when Northern Ireland minister and significant party figure Steve Baker rowed in behind Mr Sunak.
Speaking to Sky News’ Sophy Ridge, he said “Boris would be a guaranteed disaster” and a “nailed on failure” – especially with an investigation by the privileges committee looming over him regarding whether he misled Parliament over Partygate.
Mr Baker added: “Voters out there love him and he’s undoubtedly a wonderful man – he lights the room when he’s in the room.
“But unfortunately, he doesn’t have that meticulous compliance of tedious rules. He just doesn’t do it. And it’s caught up with him.
“And I’m afraid whatever people would like to be true, we need to just ruthlessly face the truth as it is. The truth as it is, is when that vote comes, which it will, his premiership would implode and this country cannot afford to be back here in a couple of months.”
Former foreign secretary Dominic Raab also said it was “difficult to see” how Mr Johnson could become prime minister again when he is “absorbed and distracted” by the issues surrounding partygate.
Speaking to Sky News, Mr Raab said he was “confident” Mr Sunak would run in the Tory leadership race and was the “standout candidate” among the field.
‘Voters must get a say’
Meanwhile, opposition parties continue to call for an immediate general election amid the ongoing turmoil within the Tory Party.
The SNP’s leader in Westminster, Ian Blackford, today wrote to Labour’s Sir Keir Starmer, urging him to work together to bring forward a vote of no confidence in the government and force a general election – though they would need support from some Tory MPs to win it.
Mr Blackford said: “The Tories have taken a wrecking ball to the UK economy and made families suffer – as mortgage rates rise, pensions fall, and soaring inflation pushes up household bills.
“Having done so much damage, they simply cannot be allowed to impose a third Tory prime minister without an election. It would be unthinkable and undemocratic. Voters must get a say.”
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