Rishi Sunak has reportedly asked Sajid Javid to step aside and support his campaign to become PM.
The former Chancellor is leading the polls to replace Boris Johnson, although Mr Javid could ruin his plans as the second most popular candidate.
Although the ex Health Secretary has yet to announce a bid for leadership, he is expected to run and wields considerable support among Tory MPs and party members.
Meanwhile, Defence Secretary Ben Wallace today revealed he will not run for office.
Mr Sunak is currently facing three other Conservative MPs in the contest, although others are expected to throw their hats in the ring today as the race heats up.
More than a dozen of Mr Sunak's colleagues have already declared their support for his campaign, putting him far ahead of his rivals Kemi Badenoch, Suella Braverman and Tom Tugendhat.
However, the race still has a long way to go and it could take up to three months before the winner takes power.
Although several Tories have voiced a desire for the race to be shortened and over much earlier than the Tory party conference in October.
Tory MP and committee chairman Sir Charles Walker said the process of selecting a new Tory leader could be "truncated" by waving regional hustings.
And leaked plans set to be approved by the Tory party next week will aim to have a new leader in place by September 5, the Telegraph reported.
Confirmed candidates
Kemi Badenoch:
Former equalities minister Kemi Badenoch announced her candidacy in The Times today.
She said she wanted to cut taxes and create a "strong but limited government" that was "focused on the essentials" in the piece.
Ms Badenoch also attacked "identity politics" and shared her plans to "reinvigorate" free speech and free markets.
Her campaign has received the backing of Lee Rowley.
The Tory MP for North East Derbyshire tweeted: "So pleased @KemiBadenoch is running and I'm proud to support her.
"Kemi's clarity of analysis about the problems our country faces and her willingness to take tough decisions are exactly why colleagues should back her. It's time for change."
Rishi Sunak:
The former Chancellor launched his "Ready for Rishi" campaign with a flashy video that detailed his rise to power.
Some speculated the clip was so slick it must have been prepared before Mr Sunak stepped down.
However his team insisted it was made in just 48 hours following his resignation.
Mr Sunak stepped down after his refusal to cut corporation tax sparked a huge row with Mr Johnson, Mail Online reports.
The former Chancellor did not reveal his vision for the country in the video, although he said he would share his plans in the "coming days and weeks".
Some 15 Tory MPs have already come out in support of Mr Sunak, despite his image taking a hit earlier this year after his wife's non-dom tax status was revealed.
His backers include Jacob Young, Angela Richardson, Bob Neill, Claire Coutinho, John Glen, Julie Marson, Kevin Hollinrake, Laura Trott, Liam Fox, Mark Harper, Mark Spencer, Mel Stride, Oliver Dowden, Paul Maynard and Robert Jenrick.
Suella Braverman:
Attorney General Suella Braverman was met with ridicule when she announced her intention to run in the race.
Shadow Attorney General Emily Thornberry joked that she was "honoured" to be opposite "the next prime minister" when she addressed Ms Braverman in the Commons.
Usually, a Cabinet minister must step down if they no longer have faith in the Prime Minister, however Ms Braverman stayed in her post while dozens of her colleagues resigned.
However, former Brexit minister Steve Baker defended Ms Braverman as he announced his support for her candidacy.
When asked why she had not spoken out sooner against the PM, Mr Baker, pointed to "collective responsibility".
He insisted Ms Braverman has the "iron resolve and authenticity" required to run the country.
Mr Baker previously hinted he may run in the race himself, although he later stepped aside and supported Ms Braverman.
Other Tory MPs who have announced their support for Ms Braverman's bid include: Jason McCartney, Desmond Swayne, Henry Smith and Robin Millar.
Tom Tugendhat:
Tom Tugendhat became the first contender to throw his hat into the ring to succeed Mr Johnson.
The chairman of the Commons Foreign Affairs Committee, who has never served in government, said he would offer the party a "fresh start".
Several Tory MPs have backed Mr Tugendhat, including Aaron Bell, Robert Largan, Damian Green, Stephen Hammond and John Stevenson.
Mr Green said: "I'm supporting Tom Tugendhat. We need a clean start, a fresh start, we need to get on with resetting the Conservative Party and resetting Government more widely in this country so that it gets back to being properly run, observing the conventions, supporting the institutions that we have in this country."
Likely candidates
Sajid Javid:
The ex Health Secretary has yet to announce his candidacy in the latest race, although he is expected to run.
According to The Times, Mr Sunak's allies have asked Mr Javid to back his campaign.
They reportedly said the pair were competing for the same voters but Mr Javid did not wield enough support or have the "infrastructure" to win.
Mr Javid was one of 10 leadership challengers in 2019.
After Mr Johnson's win, the PM made him Chancellor but the relationship quickly soured, with Mr Javid resigning in February 2020 after he was told to fire his advisers.
He was on the back benches for most of the pandemic before returning to the Cabinet as Health Secretary.
However, he was the first to quit the Cabinet this week, sending shockwaves through Westminster and triggering Mr Johnson's eventual downfall.
Jeremy Hunt:
The former Cabinet Minister, 55, was the last candidate standing against Boris Johnson in 2019.
He spent months in a "will he, won't he" tussle before coming out on the day of the Tory no confidence vote in Mr Johnson in June.
Mr Hunt said "I will be voting for change" because otherwise the Tories "are set to lose the next general election ".
Britain's longest-serving Health Secretary sparked fury on the left for pushing through junior doctor contracts that were deemed dangerous.
But in Tory eyes he is near the moderate, internationalist centre of the party, serving in a string of top roles, backing Remain and now chairing the Health Committee.
An MP since 2005, he was educated at £41,000-a-year public school Charterhouse and is a millionaire after founding the educational firm Hotcourses in 1990.
He and his Chinese-born wife, who he mistakenly said was Japanese in a bizarre 2018 gaffe while Foreign Secretary, have spent millions on a portfolio of luxury flats. He broke ethics rules by failing to declare his stake for six months.
Liz Truss:
Britain's first female Foreign Secretary has been on a journey since she branded the level of cheese imports a "disgrace" while a Remainer Environment Secretary in 2014.
Cast back even further and she was born into a lefty family, chanting 'Maggie Maggie Maggie, out out out' with her mother and later protesting Tory policy as a Lib Dem activist.
The comprehensive-schooled MP has since become a darling of some sections of the Tory right, boasting the benefits of Brexit while International Trade Secretary and failing to defend judges who were branded "enemies of the people" when she was Justice Secretary.
She has never confirmed she is running for leadership but it's a running joke in Westminster.
She poses for carefully-choreographed social media posts, including jogging on the Brooklyn Bridge and posing in a tank like Margaret Thatcher.
The 46-year-old became an MP in 2010 after working at Shell, Cable and Wireless, and then as deputy director of the Reform think tank.
She has had to defend Tory tax rises but spoke out against a windfall tax on oil giants and insists she is a low-tax Tory.
Penny Mordaunt:
Back in government since February 2020, the 49-year-old Trade Minister has kept her head down but is widely thought to hold ambitions for leadership.
The Royal Navy reservist has trodden a diplomatic path, supporting Brexit while opposing bids to oust Theresa May in 2018.
But she also has a sense of humour - she took part in a reality TV show Splash and used the word “c**k” six times in a Commons debate as part of a game with fellow reservists.
Born to an ex-paratrooper, named after a Navy ship and related to both Angela Lansbury and Labour's first chancellor Philip Snowden, she was educated at a Catholic school, a drama school and Reading University.
Since becoming an MP in 2010 she has worked in a string of top jobs including Defence Secretary but was sacked from the Cabinet by Boris Johnson - only to be brought back at a more junior rank.
Nadhim Zahawi:
The 55-year-old had a remarkable life story before being named Vaccines Minister during Covid, then Education Secretary.
He was promoted to Chancellor to replace Rishi Sunak in Boris Johnson's desperate last ditch reshuffle - before turning on the PM and saying he needed to go.
His Kurdish parents fled Baghdad when he was nine and he was educated at a West London comprehensive, then a private school before attending UCL and building up a lucrative business career.
He co-founded the leading pollster YouGov before being elected to Parliament in 2010, and had a lucrative career with the oil industry, being paid more than £1,000 an hour by Gulf Keystone Petroleum before he took a ministerial job.
Last year the Mirror disclosed he, his wife and their companies had built a £100m property portfolio. In 2013 he promised to repay a bill for power at his stables which was funded by taxpayers.
Priti Patel:
To her admirers the 50-year-old MP since 2010 is the ultimate Tory success story, inspired into politics by Margaret Thatcher after being raised by a Ugandan-Indian family in London and moving from PR into politics.
To her critics she is a hardline right-winger who has led repeated attacks on refugees and the right to protest while Home Secretary.
Even then, her failure to stem the numbers of desperate people crossing the Channel in small boats - including with a legally contentious plan to force them to Rwanda - could count against her with Tory MPs.
She was forced out as Theresa May's Trade Secretary in 2017 for holding off-the-books meetings during a holiday to Israel, which it was claimed broke the Ministerial Code. She was accused again of breaking the Code over bullying claims but exonerated by Boris Johnson, who overturned an ethics advisor's recommendation.
The Home Secretary showed her loyalty to Boris Johnson by chivvying MPs on a Tory WhatsApp group that they needed to get behind him. But she is said to be considering a leadership bid this time around.
Nadine Dorries:
Johnson loyalist Nadine Dorries is considering throwing her hat into the ring.
Ms Dorries is reportedly "seriously thinking about" running in a bid to keep Mr Johnson's "flame alive", her friends told the Mail.
Rehman Chishti:
The MP for Gillingham and Rainham said he is "actively considering" running for leader.
The newly-appointed Foreign Office minister, who became an MP in 2010, said the country needs leaders who "best reflect modern Britain" and can fix the challenges facing the nation.
He added: "As someone who came to our great country at the age of six not speaking a word of English... our country is a land of opportunity for all and I want everyone to get the best chance in life possible."
Ruled out
Ben Wallace:
The 52-year-old Defence Secretary is a favourite with Tory grassroots, regularly topping the popularity polls for influential blog ConservativeHome.
However, he today announced he would not run in the leadership contest.
He tweeted: "After careful consideration and discussing with colleagues and family, I have taken the decision not to enter the contest for leadership of the Conservative Party. I am very grateful to all my parliamentary colleagues and wider members who have pledged support.
"It has not been an easy choice to make, but my focus is on my current job and keeping this great country safe. I wish the very best of luck to all candidates and hope we swiftly return to focusing on the issues that we are all elected to address."
Steve Baker:
The former Brexit minister has ruled himself out of the leadership race after realising he would not be able to win.
He told BBC Breakfast: "I was realistic that without cabinet experience it's difficult for anyone to get into the last two.
"As much as I'd like to seriously run I'll get the PM I want with Suella Braverman.
"I would've been a candidate without any hope of reaching the last two, I don't want to waste the public's time or indeed MPs' time by standing when I wouldn't make the last two."
Michael Gove:
Boris Johnson's ally turned rival has held a string of cabinet posts but was brutally sacked by the PM in one of his last acts before admitting defeat.
Michael Gove famously torpedoed Mr Johnson's 2016 leadership bid by announcing he would run himself but he was knocked out before the members ballot.
Theresa May later triumphed after Andrea Leadsom withdrew from the contest.
Mr Gove ran again in 2019 but he is not expected to have a third tilt at the top job.
Dominic Raab:
The Deputy Prime Minister, 48, made it to the third round of the 2019 leadership contest after rising through the ranks as a Brexiteer.
But he is also expected to sit this contest out.
There have been calls for Mr Raab to take over as a caretaker PM, after he deputised for Mr Johnson when he was hospitalised with Covid.
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James Cleverly:
The newly appointed Education Secretary ruled himself out of this race as his wife is undergoing cancer treatment.
Asked if he would be running by Sky News, he said: "No, I won't be.
"I put myself forward last time, I don't regret that, I really enjoyed it. As you know, my wife has been going through cancer treatment and whilst that is progressing, well, it hasn't concluded.
"It's not the right time for me."
