Boris Johnson will need the support of at least 100 Tory MPs if he is to make a spectacular comeback to replace Liz Truss who quit as Tory leader after just 44 days in No 10.

Ms Truss’s resignation, signalling the end of the shortest term by any prime minister, followed a botched financial statement, the loss of two of her most senior Cabinet ministers and an open revolt by Tory MPs.

The Conservatives will now scramble to elect a replacement by the end of next week.

Allies of former leader Mr Johnson pushed for him to make a return, less than two months after leaving office, while Rishi Sunak, who defeated Ms Truss among MPs in the last contest, is widely expected to stand.

In an attempt to fast-track the process – and potentially eliminate the need for a vote among members – candidates will need the support of 100 of the 357 Tory MPs in Parliament to make it onto the ballot paper.

In the final ballot of the last contest, Mr Sunak had 137 votes, Ms Truss 113 and Penny Mordaunt – who would also be expected to stand again – 105.

Johnson loyalists were quick to say the former premier, who quit in a mire of sleaze, was the best choice to lead the party out of its current difficulties.

Former culture secretary Nadine Dorries said she had spoken to Mr Johnson – currently thought to be holidaying in the Caribbean –  following Ms Truss’s statement, hinting strongly that he had decided 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.

Trade minister Sir James Duddridge said he hoped Mr Johnson had enjoyed his holiday but it was “time to come back” as there were a “few issues at the office that need addressing”.

But in a sign of how divisive the former premier is, Tory veteran Sir Roger Gale pointed out Mr Johnson was still being investigated for potentially lying to MPs over the partygate scandal.

“Until that investigation is complete and he is found guilty or cleared, there should be no possibility of him returning to Government,” Sir Roger said.

Ms Truss’s announcement came a little over 24 hours after insisting she was “a fighter, not a quitter”.

She recognised she “cannot deliver the mandate” as a low-tax, pro-growth premier which Tory members gave her in September when she replaced Mr Johnson.

Her announcement followed talks with the chairman of the 1922 Committee of backbench Conservatives, Sir Graham Brady, where it became clear she could not hope to carry on after losing the support of her MPs.

The Prime Minister, accompanied by husband Hugh O’Leary, said a short leadership contest “will ensure that we remain on a path to deliver our fiscal plan and maintain our country’s economic stability and national security”.

“I will remain as Prime Minister until a successor has been chosen.”

Tory leadership hopefuls know they will face a daunting task to revive the party’s fortunes.

Sir Graham and party chairman Sir Jake Berry set out the process, with nominations for MPs open until 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.

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.

Some of the party’s big hitters ruled themselves out, with Chancellor Jeremy Hunt focusing on calming the financial markets, James Cleverly making the case to stay on as Foreign Secretary and Michael Gove resisting another run.

Commons Leader Penny Mordaunt was in the Chamber as news of Ms Truss’s resignation broke and told MPs she would “keep calm and carry on”.

Justice Secretary Brandon Lewis has been encouraged to stand by colleagues, allies said.

Sir Graham said the process could be concluded by October 28 as “we’re deeply conscious of the imperative in the national interest of resolving this clearly and quickly”.

He added: “We fixed a high threshold but a threshold that should be achievable by any serious candidate who has a prospect of going through.”

The contest to replace Mr Johnson lasted longer than Ms Truss’s premiership, paralysing the Government at a time of a cost-of-living crisis.

Labour leader Sir Keir Starmer demanded a general election “now” so that the nation can have “a chance at a fresh start”.

Sir Keir said: “The British public deserve a proper say on the country’s future. They must have the chance to compare the Tories’ chaos with Labour’s plans to sort out their mess, grow the economy for working people and rebuild the country for a fairer, greener future.”

Ms Truss’s leadership had been on life support since the markets turned against her following the September 23 mini-budget which promised £45 billion of unfunded tax cuts on top of a massively expensive energy support package.

Axing chancellor Kwasi Kwarteng and abandoning most of the plans helped calm the turmoil – as did an emergency intervention in the bond markets by the Bank of England – but left her premiership holed below the waterline.

Wednesday’s chaos, which saw Suella Braverman resign as home secretary, officially for using a personal email to send a sensitive document but also while she was at odds with the Prime Minister over immigration policy, added to the pressure on Ms Truss.

And the ugly scenes in the Commons as Tory MPs were threatened with having the whip suspended if they rebelled over fracking were the final straw for many Conservatives.

The number of Tory MPs publicly demanding Ms Truss’s resignation doubled before lunch was over on Thursday, taking the total to 15, but a far greater number were privately agitating for her exit, as Sir Graham made clear to the Prime Minister.