Commons leader Penny Mordaunt has said she is running to replace Liz Truss as Conservative party leader and prime minister.
She is the first Conservative MP to officially throw her hat into the ring, and has promised to "unite the country, deliver our pledges" and win the next general election.
Announcing her bid, she tweeted: “I’ve been encouraged by support from colleagues who want a fresh start, a united party and leadership in the national interest.”
Ms Mordaunt has already held talks with Jeremy Hunt and assured him he can stay on as chancellor if she becomes prime minister, it is understood.
She also assured Mr Hunt she would deliver the medium-term fiscal plan as proposed on October 31, according to a source close to the Commons leader.
The Portsmouth North MP, aged 49, finished third in the previous Tory leadership contest held over the summer.
Her initial bid for the top job triggered some excitement, as colleagues rallied behind a fresh face to lead the Conservatives.
The announcement comes as the Tory party fights to restore its credibility and to heal its own internal divisions after Ms Truss' short-lived premiership sent financial markets into a panic and the value of the pound crashing.
Within the hour of Ms Mordaunt's announcement, several Tory MPs declared their support, including MP for Penrith and The Border Neil Hudson, who said she has the "leadership attributes, experience, empathy and compassion to unite our country".
Nicola Richards, MP for West Bromwich East, said she believes Ms Mordaunt will be the “stabilising, calm and collected figure” needed to “see us through the turbulent times ahead”.
Harriett Baldwin, MP for West Worcestershire, Bob Seely, MP for the Isle of Wight, and Caroline Dinenage, MP for Gosport, also expressed their support.
Meanwhile former chancellor Rishi Sunak - who finished second to Ms Truss in the last leadership race - is also gaining supporters.
Among them is forner veterans minister Johnny Mercer, who announced his backing on BBC Radio 4 this evening.
Former chancellor and health secretary Sajid Javid also threw his weight behind Mr Sunak, tweeting: "Our responsibility as public servants is to make decisions in the national interest, especially at a time like this.
"Our country desperately needs economic stability, hard-headed decision making and strong leadership.
"It is abundantly clear that Rishi Sunak has what it takes to match the challenges we face - he is the right person to lead our party and take the country forward.
"I also believe it is in the national interest to have a strong Conservative Party. The only way for our party to reclaim our values and recover our reputation for stewardship is to move on from mistakes of the past and come together to focus on the future."
Potential candidates appear to be mulling their options, but Boris Johnson's bid may be gathering pace before it has been confirmed - Carl Dinnen reports
Boris Johnson is also expected to make a bid to return as prime minister, and has been backed by Ben Wallace, the first senior minister to publicly state his support.
The defence secretary ruled himself out of the contest to replace Liz Truss, who resigned on Thursday after weeks of financial turmoil sparked by her mini-budget.
"At the moment, I would lean towards Boris Johnson," he said, adding he has "questions to answer" around the partygate investigation that kicks off next month.
“This will be potentially our third prime minister since the general election of 2019, that means we have to think about that legitimacy question that the public will be asking themselves, and also about who could win the next election – that’s obviously important for any political party at the time,” he said.
“So at the moment, I would lean towards Boris Johnson.
"I think he will still have some questions to answer around, obviously, that investigation, but I know when I was Secretary of State for Defence, he invested in defence, he supported me, he supported the actions this country has taken to keep us safe.”
It makes him the third member of Liz Truss's cabinet to back the former PM, including levelling up secretary Simon Case and business secretary Jacob Rees-Mogg.
It comes just six weeks after Mr Johnson left No 10 for the final time, forced out by his own MPs after one scandal too many, allies are urging him to run again for a second shot at the Tory crown.
If he does, he is likely to find himself up against Mr Sunak – who is blamed by Mr Johnson’s supporters for bringing him down.
Such a move would be highly divisive within the Conservative Party, with reports some MPs could resign the whip and sit as independents rather than serve under Mr Johnson.
But his supporters argue that he alone of the potential candidates to be the new prime minister has won a general election and has a mandate from the British public.
The target of 100 MPs is believed by many in Westminster to be beyond him - but according to some trackers, he's already received the backing of around 50 MPs, including former supporter and Business Secretary Jacob Rees-Mogg.
There was no immediate word from Mr Johnson – who was thought to be holidaying with his family in the Caribbean – on his intentions.
However, diehard loyalist Nadine Dorries, the former culture secretary, said she had spoken to him following Ms Truss’s resignation and hinted strongly that he was preparing to run.
“He is a known winner and that is certainly who I’m putting my name against because I want us to win the general election. Having a winner in place is what the party needs to survive,” she told Sky News.
Veteran backbencher Sir Roger Gale, a long-time critic of Mr Johnson, however warned that if he succeeds he could be met with a wave of resignations by Tory MPs.
“I think that there would be people, indeed like myself, who would find ourselves in the awful position of having to resign the Conservative whip,” he told Times Radio.
Selecting Mr Johnson as Tory leader would be “absolutely catastrophic”, Foreign Office minister Jesse Norman added.
The Tory MP tweeted: “There are several very good potential candidates for Conservative leader. But choosing Boris now would be - and I say this advisedly - an absolutely catastrophic decision.”
And former environment secretary under Mr Johnson, George Eustice, said "you can't turn the clock back" as he confirmed his support for Mr Sunak.
But Mr Johnson's father, Stanley, told ITV's Good Morning Britain that his son was "on a plane," speaking on Friday morning.
However Mr Johnson senior was unable to confirm if the former prime minister was coming back early in order to stand in the leadership contest.
'A man that his own party has declared unfit for office' - Starmer
Labour leader Sir Keir Starmer, who called for an immediate general election, said: "To go from the kamikaze budget under Liz Truss to a man that his own party has declared unfit for office is the most powerful argument you could possibly have for a general election."
For critics, a comeback would be particularly problematic as Mr Johnson still faces an investigation by the Commons Privileges Committee over claims he lied to Parliament over lockdown parties in Downing Street, which could potentially see him expelled as an MP.
He will be expected to give evidence to the inquiry over the next few weeks.
Former home secretary and party leader Michael Howard, who lost the 2005 general election to Tony Blair, declared his support for Mr Sunak, saying that Boris Johnson had "had his chance."
He also suggested that Ms Mordaunt has "an important role to play in the new administration," but concluded that Mr Sunak is "better qualified at this particular moment in our affairs to become Prime Minister."
Boris has "had his chance" says former leader Michael Howard, who backs Rishi Sunak
Other names in the frame include Suella Braverman, who resigned as Liz Truss's Home Secretary following a security breach.
She told Sky News on Friday morning she would make a statement on her position "in due course."
International Trade Secretary Kemi Badenoch's name is also being touted – but despite standing in the last contest both her and Ms Braverman may struggle to get the nominations.
Under the rules set out by Sir Graham Brady – the chairman of the backbench 1922 Committee – and party chairman Sir Jake Berry, nominations will close at 2pm on Monday.
The first ballot of MPs will then be held between 3.30pm and 5.30pm on Monday – if there are three candidates with the required number of nominations the loser will be eliminated.
There will also be a hustings of candidates on Monday, before MPs vote, according to Sir Graham Brady.
Once there are two candidates remaining, an indicative vote will be held so that the party membership know which is the preferred option among MPs.
Members will be able to take part in an online vote to choose their next leader and the country’s prime minister with the contest due to conclude by October 28.
The rules appear designed to encourage the candidate who finishes second to stand aside for the winner, ensuring the new leader has the support of the majority.
But few believe that if that is Mr Johnson – who remains hugely popular among ordinary members – he would do so.
Tory grandee Sir Geoffrey Clifton-Brown, however, said it was important that the new leader commanded as much support as possible among the MPs.
“It is the Members of Parliament who have to work with a prime minister and I think it is very, very important that as many Members of Parliament are satisfied with the candidate,” he told BBC2’s Newsnight.
Meanwhile, Conservative MP Andrew Mitchell has said the Tory politicians needed to stop “establishing tribal gangs who support a particular leader so that they can get a job in the Cabinet or Government regardless of their abilities”.
Writing in The Daily Telegraph, Mr Mitchell said: “This unedifying way of conducting politics is harming the business of government and indeed the country.”
Ms Truss’s resignation on Thursday after just 44 days in office brings to an end the shortest premiership in British history.
It followed weeks of financial and political turmoil in the wake of then chancellor Kwasi Kwarteng’s calamitous £45 billion mini-budget giveaway which led to a collapse in support for Ms Truss among Tory MPs.
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