Rishi Sunak has announced his bid to become the next Conservative leader and prime minister, six weeks after Liz Truss beat him to the top job.

The former chancellor has put himself forward for the second time in a matter of months after the extraordinary resignation of Ms Truss on Thursday, 44 days into her premiership.

In a tweet announcing his candidacy, Mr Sunak said the UK faces “a profound economic crisis”, adding: “The choice our party makes now will decide whether the next generation of British people will have more opportunities than the last.

“That’s why I am standing to be your next prime minister and leader of the Conservative Party. I want to fix our economy, unite our party and deliver for our country.”

The race to be Tory leader – next UK prime minister latest updates

To be included on the ballot paper, leadership candidates need support from at least 100 Conservative MPs by Monday, and Mr Sunak had already clocked up 124 before announcing he was running.

So far, the only other hopeful to officially confirm they are taking part is Commons Leader Penny Mordaunt, who has 24 public backers.

She told Sky News that the country deserves a leader who “understands the life they lead”, adding: “What this country needs is a fresh face, someone that can unite the Conservative Party and get things to work in this country.”

But it is thought former Prime Minister Boris Johnson will also make a bid for the leadership again, with close allies claiming he already has the numbers to make the ballot – despite only 57 MPs publicly declaring for him so far.

Tory MP and Johnson backer David Morris told Sky News: “We will just have to wait until tomorrow when Boris declares” – though later said he could not confirm the announcement would take place.

Mr Sunak and Mr Johnson held talks late last night as speculation grew the pair could do a deal to secure the premiership and get the party to unite behind them.

But Mr Johnson’s former deputy prime minister – who is now backing Mr Sunak – Dominic Raab told the BBC he did not think a deal had been done, adding: “That’s not the right way to proceed.”

Theresa May’s de-facto deputy, Tory MP Damian Green, warned against a “stitch up” between the pair and threw his backing behind Ms Mordaunt, saying she was “attracting support from all wings of the party” and would create “calm stability” for the Conservatives.

The ex-chancellor’s Twitter statement made no mention of his former boss, instead saying to the public: “I served as your chancellor, helping to steer our economy through the toughest of times.

“The challenges we face now are even greater. But the opportunities – if we make the right choice – are phenomenal.”

Mr Sunak also said he had a “track record of delivery” and “a clear plan to fix the biggest problems we face”, as well as promising to deliver of the Conservatives’ last manifesto.

And he added: “There will be integrity, professionalism and accountability at every level of the government I lead and I will work day in and day out to get the job done.”

But the Liberal Democrats’ deputy leader, Daisy Cooper, said he “cannot be trusted to steer our country through this cost of living crisis”, adding: “He was the Chancellor that hiked taxes on hardworking families and lost billions of pounds of taxpayers money to COVID contract fraud.”

She reiterated calls from opposition parties for an immediate general election, and said: “The future of our country should be in the hands of voters, not the Conservative MPs who have caused all this chaos.”

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Among those who have publicly voiced their support for Mr Sunak are: Kemi Badenoch, the international trade secretary; Grant Shapps, the home secretary; Steve Barclay, the former health secretary; Lord Frost, former Brexit minister; Dominic Raab, the former foreign secretary; and Sajid Javid, the former health secretary.

Northern Ireland minister Steve Baker also announced his support for the former chancellor to Sky News’ Sophy Ridge this morning, while launching a scathing attack on a second Johnson premiership – saying it would be “a guaranteed disaster”.

He pointed to the investigation Mr Johnson was facing in Parliament about whether he misled MPs over what he knew about the Partygate scandal, as if found guilty, he could face a suspension or even a recall petition if he is suspended for 10 days or more.

But Mr Baker’s boss, Northern Ireland Secretary Chris Heaton-Harris, insisted to Ridge that Mr Johnson was “a great unifier” and “a great campaigner” who had “a solid sense of what the country wants to hear and what the country needs to happen”.

Labour’s Lisa Nandy said it was “extraordinary watching Tory MPs who put in letter of no confidence in him just a few weeks ago saying he wasn’t fit to hold the highest office now talking openly about trying to bring him back”.

She told Ridge it was “a sign of absolute utter desperation in the Tory party”, and reiterated opposition calls for an immediate general election.

In the last leadership election after Mr Johnson was ousted from Number 10 over his handling of allegations against his deputy chief whip, Mr Sunak had 137 nominations, Ms Truss 113 and Ms Mordaunt 105.

But the former chancellor lost to Ms Truss in the final round of voting by Tory members.

Ms Truss won on a mandate to slash taxes to boost economic growth, but this proved to be her downfall after her mini-budget unleashed turmoil in the financial markets, sent the pound to record lows against the dollar and forced the Bank of England to intervene.

She was eventually forced to row back on almost all of her pledges after sacking Kwasi Kwarteng as chancellor and appointing Jeremy Hunt, a Sunak ally, to restore economic stability.

During the previous contest, Mr Sunak called the tax cuts proposed by Ms Truss “immoral” and warned about the need for fiscal responsibility.