The second Tory leadership race in just three months is underway following the extraordinary resignation of Liz Truss.

The now-outgoing PM was forced from office after just 44 days following a seismic few weeks in Westminster that saw her tax-slashing mini-budget crash and burn.

Ms Truss’s resignation, signalling the end of the shortest term by any prime minister in modern British history, followed a raft of humiliating U-turns, the loss of two of her most senior Cabinet ministers and an open revolt by Tory MPs.

All eyes are now on who could replace her – with speculation mounting that Boris Johnson could launch a spectacular comeback to frontline politics, just six weeks after he was officially ousted from the top job.

Party rules for the new leadership contest mean PM hopefuls would need the backing of at least 100 Tory MPs by Monday afternoon to face off against any other successful challenger in a vote of the membership.

This will rule out a number of candidates from running and means the maximum number of people able to stand is three.

Sir Graham Brady, chairman of the powerful 1922 backbench committee, said: “We fixed a high threshold but a threshold that should be achievable by any serious candidate who has a prospect of going through.”

Who are the runners and riders?

Tory MPs are scrambling to find a replacement who can unite the party and turn around its fortunes after a series of dire polls predicted electoral wipe out.

The new inhabitant of No 10 faces a daunting set of challenges – from the cost of living crisis and rising energy bills to resolving the Northern Ireland protocol row, and war in Ukraine.

Although big hitter Jeremy Hunt has already ruled himself out of the running, there are other Tory MPs who appear to be waiting in the wings.

Sky’s deputy political editor Sam Coates says former chancellor and Tory leadership finalist Rishi Sunak has signalled he is “very, very up for the job”.

Commons leader Penny Mordaunt has also “been making it clear in her public appearances that she’s up for the job”.

And Suella Braverman – who resigned as home secretary on Wednesday– was highly critical of Ms Truss when she stepped down, in a move that allies believe shows she is also keen to step up to the plate.

Coates says: “The question now is who will stand aside and who will survive in an intense, week-long leadership contest.”

Nominations opened on Thursday and will close at 2pm on Monday – with a new leader to be chosen by Friday 28 October.

The final two candidates will take part in a hustings event organised with news broadcasters, before an online vote for members to choose who they want to lead the party.

However, we could have a new leader sooner than that.

One potential option is that MPs coalesce around one candidate, meaning the contest will be over on Monday if only one person is able to receive enough nominations.

‘Bring back Boris’

On Thursday night, momentum appeared to be swinging behind Boris Johnson amid reports he will throw his hat in the ring.

Former culture secretary Nadine Dorries, a staunch Johnson ally, told Sky News she is confident he will meet the 100 MPs threshold.

“There is only one MP who has the mandate of the British public, who won a general election only three years ago with an 80-seat majority, and that was Boris Johnson,” Ms Dorries said.

“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.”

While multiple Tory MPs have expressed their support for a Johnson comeback, any attempt to return to frontline politics is proving divisive.

Senior backbencher Sir Roger Gale MP tweeted to remind people that the ex-prime minister, who resigned in a mire of sleaze, was still under investigation by the Privileges Committee for potentially misleading the House over partygate.

If found guilty, Mr Johnson could face recall proceedings that would leave him battling for his seat in the Commons if he receives a suspension of 10 days or more.

Sir Roger told Times Radio that, if Mr Johnson is voted back in as PM, he would resign from the Conservative party whip and stand as an independent.

Read More:
Resignations, reversals and rebellion – the 44 days of Liz Truss’s premiership
The divided Tories won’t find it easy choosing a new PM

Could Boris Johnson reach 100 nominations?

There are currently 357 Conservative MPs, 148 of whom voted against Mr Johnson in a confidence vote just a few months ago.

If they refuse to back him again, that leaves 209 MPs to choose from.

Liz Truss had 113 nominations this summer, so these are all up for grabs.

Brenden Clark-Smith, the Conservative MP for Bassetlaw, is among the group calling to “bring back Boris”.

However, problems with a Johnson candidacy include his popularity with the public crashing – even if he still rides high with the Tory membership.

Polling for the Conservatives was already dropping during Mr Johnson’s premiership as it became beset with scandals, including the ex-PM breaking his own lockdown laws.

Mr Johnson was ultimately forced to announce his resignation on 7 July as Cabinet allies turned on him with a series of resignations.

The final straw was questions about his judgment over Chris Pincher, the then-Tory whip who was the centre of drunken groping allegations. That came on top of Mr Johnson’s attempts to change the rules to prevent the suspension of then-Conservative MP Owen Paterson after he broke lobbying rules.

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Ms Truss officially took over from Mr Johnson on 6 September, with members favouring her tax-slashing plan for growth over Mr Sunak’s more conservative fiscal policies.

But just two weeks into the job, her disastrous mini-budget sparked chaos in the financial markets, leading to the sacking of chancellor Kwasi Kwarteng and a humiliating abandonment of the very economic policies that brought her into office.

Many MPs have voiced their support for Mr Sunak – who had warned Ms Truss that her economic policies were “immoral” and campaigned for fiscal responsibility during the last leadership race.

Jonathan Djanogly and Mark Garnier both tweeted their support for him late on Thursday night.

Richard Holden MP said that in the “difficult economic times, the party and the country needs a PM who has got the economic experience to deliver real stability over the next few years and get the ship of state back on an even keel – and that person is Mr Sunak”.

‘Last chance saloon’

A vicious leadership contest would further divide an already split party which is about to see its third prime minister in the space of a few months – and many Tory MPs are calling for colleagues to unite behind the next leader, whoever that may be.

Justin Tomlinson said the leadership contest is the “last-chance saloon” for the party to maintain credibility, while former cabinet minister Robert Jenrick, warned the Tories face “extinction…if we get this wrong”.

Opposition parties say that, whoever is handed the keys to Downing Street, a general election must be called immediately.

Labour leader Sir Keir Starmer said the Conservative Party has “shown it no longer has a mandate to govern”, adding that British people “deserve so much better than this revolving door of chaos”.