Outgoing British Prime Minister Boris Johnson faces more pressure from his party to depart immediately rather than remain in a “caretaker” position until a new leader is elected.

A growing number of Tory MPs say Mr Johnson should leave Downing Street now rather than hang around for the weeks or months it could take to replace him as prime minister.

Party officials are expected to announce on Monday (local time) a timetable for electing Mr Johnson’s replacement and some MPs have said they might throw their hat in the ring including Transport secretary Grant Shapps and former health secretary Sajid Javid.

It follows Mr Johnson finally falling on his sword on Thursday night (Australian time) after a dramatic few days in which more than 60 government figures resigned — nearly half the payroll.

The historic mutiny, the likes of which had never been seen before and which Mr Johnson characterised as the “herd” moving, forced him out of the “best job in the world” even while he determinedly tried to cling onto power.

In a speech outside No 10, announcing he would step aside, Mr Johnson said the reason he fought so hard over the last few days was to continue to deliver his mandate from the 2019 election landslide.

Boris Johnson addresses the nation, saying he will step aside. Photo: Getty

The scandal-ridden PM said he tried to persuade his colleagues it would be “eccentric” to change governments when “we’re actually only a handful of points behind in the polls”.

“And I regret not to have been successful in those arguments, and of course it’s painful not to be able to see through so many ideas and projects myself,” he said.

“But as we’ve seen at Westminster the herd instinct is powerful and when the herd moves, it moves.

“And my friends, in politics, no one is remotely indispensable, and our brilliant and Darwinian system will produce another leader, equally committed to taking this country forward through tough times.”

Carrie Johnson and daughter Romy during Mr Johnson’s speech outside No 10. Photo: Getty

Mr Johnson said he had appointed a cabinet until a new leader was in place and he too would continue to serve until then.

“It was a short and bizarre resignation speech which didn’t mention the word resign or resignation once. There was no apology, no contrition,” Conservative MP Andrew Bridgen said.

“There was no apology for the crisis his actions have put our government, our democracy, through.”

Opponents and many in his own party said Mr Johnson should leave immediately and hand over to his deputy, Dominic Raab.

Former Conservative prime minister John Major said it was “unwise and maybe unsustainable” for him to remain in office when he could still exert its powers.

“For the overall wellbeing of the country, Mr Johnson should not remain in Downing Street — when he is unable to command the confidence of the House of Commons — for any longer than necessary to effect the smooth transition of government,” Major said in a letter released to media.

Keir Starmer, leader of the main opposition Labour Party, said he would call a parliamentary confidence vote if the Conservatives did not remove Mr Johnson at once.

The public gathers outside Downing Street with cheers and boos. Photo: Getty

The crisis comes as people in the UK are facing the tightest squeeze on their finances in decades after the COVID-19 pandemic, with soaring inflation and the economy forecast to be the weakest among major countries in 2023 apart from Russia.

It also follows years of internal division sparked by the narrow 2016 vote to leave the European Union, and threats to the make-up of the United Kingdom itself with demands for another Scottish independence referendum, the second in a decade.

Support for Mr Johnson had evaporated during one of the most turbulent 24 hours in recent UK political history, epitomised by finance minister Nadhim Zahawi, who was only appointed to his post on Tuesday, calling on his boss to resign.

Mr Zahawi and other cabinet ministers went to Downing Street on Wednesday evening, along with a senior representative of those MPs not in government, to tell Johnson the game was up.

Initially, Mr Johnson refused to go and seemed set to dig in, sacking Michael Gove — a member of his top ministerial team who was one of the first to tell him he needed to resign — in a bid to reassert his authority.

But by Thursday morning as a slew of resignations poured in – including that of Michelle Donelan who he had appointed education secretary only on Tuesday night — it became clear his position was untenable.

Who could be the next PM?

Several Conservative politicians are in the frame to challenge for the Briitsh prime ministership after a turbulent two and half years.

However, there is no clear favourite and the timeframe for appointing a new leader has not been revealed yet.

LIZ TRUSS

The foreign secretary is the darling of the ruling Conservative Party’s grassroots and has regularly topped polls of party members carried out by the website Conservative Home.

Ms Truss has a carefully cultivated public image and was photographed in a tank last year, echoing a famous 1986 photo of Britain’s first female prime minister, Margaret Thatcher.

The 46-year-old spent the first two years of Mr Johnson’s premiership as international trade secretary, championing Brexit, and last year was appointed as Britain’s lead negotiator with the European Union.

Ms Truss said on Monday that Mr Johnson had her “100 per cent backing” and she urged colleagues to support him.

JEREMY HUNT

The former foreign secretary, 55, finished second to Mr Johnson in the 2019 leadership contest. He would offer a more serious and less controversial style of leadership after the turmoil of Johnson’s premiership.

Over the last two years, Mr Hunt has used his experience as a former health secretary to chair parliament’s health select committee and has not been tarnished by having served in the current government.

Earlier this year, he said his ambition to become prime minister “hasn’t completely vanished”. Mr Hunt said he voted to oust Johnson in a confidence vote last month that the prime minister narrowly won.

BEN WALLACE

Defence minister Ben Wallace, 52, has risen in recent months to be the most popular member of the government with Conservative Party members, according to Conservative Home, thanks to his handling of the Ukraine crisis.

A former soldier, he was mentioned in dispatches in 1992 for an incident in which the patrol he was commanding captured an Irish Republican Army guerrilla unit suspected of trying to carry out a bomb attack on British troops.

He began his political career as a member of Scotland’s devolved assembly in May 1999, before being first elected to the Westminster parliament in 2005.

He was security minister from 2016 until taking on his current role three years later, winning plaudits as his department evacuated British nationals and allies from Afghanistan last year, and for sending weapons to Kyiv.

RISHI SUNAK

Mr Sunak, who resigned as finance minister on Tuesday saying the British public “rightly expect government to be conducted properly, competently and seriously”, was until last year the favourite to succeed Mr Johnson.

He was praised for a COVID-19 economic rescue package, including a costly jobs retention programme that averted mass unemployment.

But Mr Sunak later faced criticism for not giving enough cost-of-living support to households. Revelations about his wealthy wife’s non-domiciled tax status and a fine he received, along with Johnson, for breaking COVID lockdown rules have damaged his standing.

His tax-and-spend budget last year put Britain on course for its biggest tax burden since the 1950s, undermining his claims to favour lower taxes.

SAJID JAVID

Mr Javid was the first cabinet minister to resign in protest over accusations that Johnson misled the public over what he knew about sexual harassment allegations against a Conservative lawmaker.

A former banker and a champion of free markets, Javid has served in a number of cabinet roles, most recently as health minister. He resigned as Johnson’s finance minister in 2020.

The son of Pakistani Muslim immigrant parents, he is a Thatcher admirer and finished fourth in the 2019 leadership contest to replace former PM Theresa May.

NADHIM ZAHAWI

The new finance minister impressed as vaccines minister when Britain had one of the world’s fastest rollouts of COVID jabs.

Mr Zahawi’s personal story as a former refugee from Iraq who came to Britain as a child sets him apart from other contenders.

He co-founded polling company YouGov before entering parliament in 2010. His last job was as education secretary. Mr Zahawi said last week that it would be a “privilege” to be prime minister at some stage.

PENNY MORDAUNT

The former defence secretary was sacked by Mr Johnson when he became prime minister after she endorsed Mr Hunt at the last leadership contest.

Ms Mordaunt was a passionate supporter of leaving the European Union and made national headlines by taking part in a now-defunct reality TV diving show.

A junior trade minister, Ms Mordaunt called the lockdown-breaking parties in government “shameful”. She had previously expressed loyalty to Mr Johnson.

TOM TUGENDHAT

The chair of parliament’s foreign affairs committee, and a former soldier who fought in Iraq and Afghanistan, has already indicated he would run in any leadership contest.

He has been a regular critic of Mr Johnson and would offer his party a clean break with previous governments.

However, he is relatively untested because he has never served in cabinet.

SUELLA BRAVERMAN

A Brexit-backing Attorney-General, Ms Braverman has indicated she will run for the leadership.

She was heavily criticised by lawyers during her tenure after the government sought to break international law over post-Brexit trade rules in Northern Ireland.

-with AAP