The race to succeed Boris Johnson as prime minister is well and truly underway after the scandal-ridden politician resigned as leader of the Conservative Party on Thursday night (Australian time).

Former UK finance minister Rishi Sunak has already declared he will be in the running, three days after helping to launch the cascade of resignations that brought the prime minister down.

“Someone has to grip this moment and make the right decisions. That’s why I’m standing to be the next leader of the Conservative Party and your prime minister,” Mr Sunak said in a campaign video released on Twitter.

Mr Johnson’s impending departure came after 60 lawmakers and government officials handed in their resignations.

He told reporters outside No.10 Downing Street that “it is clearly now the will of the parliamentary Conservative Party that there should be a new leader, and therefore a new prime minister”.

But the outgoing PM has infuriated colleagues by insisting he remain in office until the Conservative Part elects a new leader.

Below, TND takes a look at why Mr Johnson was forced to resign – and reviews the likely frontrunners in the race to succeed him.

Why did Boris Johnson resign?

Mr Johnson and the Conservative Party were victorious in a landslide election in 2019, earning a substantial majority of the vote after pledging to ‘Get Brexit Done’.

Mr Johnson hoped the momentum would continue into 2020.

But the COVID pandemic quickly soured Mr Johnson’s popularity, with a long list of scandals repeatedly bringing his integrity into question.

The first major criticism was that his government had fumbled their initial pandemic response, having been slow to bring in restrictions and consequently allowing the virus to circulate.

Mr Johnson declined to attend several meetings in the early days of the pandemic.

Later, a parliamentary report published in October 2021 found the government’s lacklustre response caused “many thousands” of avoidable deaths.

The Prime Minister has since faced months of damaging revelations about illegal gatherings at his Downing Street residence during his government’s pandemic lockdowns.

Dubbed ‘partygate’, footage and images emerged in late 2021 and early 2022 that showed Mr Johnson taking part in alcohol-fuelled gatherings, while the rest of the country remained in tight lockdowns.

Mr Johnson even issued an apology to the Queen after it emerged he had hosted a party on the eve of Prince Phillip’s funeral, an event at which even the monarch had to sit alone due to strict COVID restrictions.

ITV news revealed photographs of Boris Johnson at a party in November 2020.

The fallout saw Mr Johnson’s popularity plummet, prompting a vote of no confidence.

Mr Johnson barely scraped through, with 40 per cent of his ministers voting against him.

But the straw that broke the camel’s back was a more recent scandal, in which Mr Johnson lied about whether he was aware of the sexual allegations made against a close political ally, Chris Pincher.

Mr Johnson appointed Mr Pincher as deputy chief whip in February. But last week it emerged Mr Pincher had been the subject of past sexual harassment allegations.

The Prime Minister said he was unaware of the allegations at the time of Mr Pincher’s appointment. But it emerged this week that Mr Johnson had, in fact, been briefed on the allegations back in 2019.

The news prompted an astonishing wave of resignations from 60 lawmakers and officials, accounting for nearly half of Mr Johnson’s payroll.

Health minister Sajid Javid said he could “no longer continue in good conscience”.

“I am instinctively a team player but the British people also rightly expect integrity from their Government,” he said.

What has been agreed on?

Mr Johnson has agreed to step down as soon as a new Conservative Party leader is chosen.

Until then, he will continue to serve as Britain’s Prime Minister.

Mr Johnson has also appointed a placeholder cabinet to serve in lieu of his many resigned ministers, an arrangement that will remain in place until a new leader is appointed.

But Mr Johnson’s decision to temporarily remain in office has been met with anger from several Tory MPs, who say he should exit office immediately, rather than wait for his replacement.

Former Conservative PM John Major said it was “unwise and maybe unsustainable” for him to remain in office.

“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,” he said in a letter released to media.

Who is likely to take his place?

The Tories will soon vote on who should become their new leader.

The winner of this vote will become both the new party leader and the prime minister, without the need for a national election.

Here are some of the likely frontrunners.

Photo: UK Parliament

BEN WALLACE

Defence minister Ben Wallace, 52, is perhaps the most obvious choice for party leader.

Mr Wallace has emerged as the favourite among Conservative Party members after winning plaudits in recent months for his part in Britain’s response to the war in Ukraine.

Mr Wallace came out on top in a snap YouGov poll, with 13 per cent of surveyed Tory members saying they would like to see him become the next Prime Minister.

But Mr Wallace was not among the dozens that resigned from Mr Johnson’s cabinet, which may ultimately come back to bite him.

Photo: UK Parliament

RISHI SUNAK

Taking a look at head-to-head polling, Mr Wallace’s closest competitor is outgoing Chancellor Rishi Sunak.

Mr Sunak, 42, was once in prime position to become party leader, but his popularity has taken a bruising in recent months.

He made headlines earlier this year when it was revealed his billionaire heiress wife had avoided millions of pounds in taxes.

Mr Sunak was also forced to reject calls for his resignation in April, when he was fined for accompanying Mr Johnson at a lockdown party at Downing Street in June 2020.

His lack of cabinet experience might also work against him should he run, having only become Chancellor in 2020.

Photo: UK Parliament

SUELLA BRAVERMAN

Suella Braverman was the first name to throw her hat in the ring for the top job, announcing her intention to run for office hours before Mr Johnson’s resignation.

Ms Braverman, 42, has served as the nation’s Attorney General since February 2020.

She said it would be “the greatest honour” to serve as Prime Minister.

“If there is a leadership contest, I will put my name into the ring,” she told ITV.

Ms Braverman has been a big supporter of Mr Johnson and Brexit during her tenure. But she was heavily criticised by lawyers when the government sought to break international law over post-Brexit trade rules in Northern Ireland.

Photo: UK Parliament

STEVE BAKER

Tory MP Steve Baker was the second minister to declare his prime ministerial intentions.

Mr Baker, 51, told the BBC that it was “time for stability”.

“We’ve got to look really seriously at who we want to be, I think the public … I’m certain the British public can rise to the challenge at the moment, we have got to deal with the economy and energy policy,” he said.

“We’ve got to make sure that the people of this country are evermore prosperous and free.”

Mr Baker runs the European Research Group, which has been credited for its key role in achieving Brexit.

The anti-green MP is also a leading member of the Net Zero Scrutiny Group.

He is a vocal critic of environmental policy, having once retweeted a report that claimed climate change was a fallacy.

Photo: UK Parliament

ELIZABETH TRUSS

Liz Truss, the country’s foreign secretary, cut short her trip to Bali for a G20 foreign ministers meeting as news broke of Mr Johnson’s resignation.

Ms Truss, 46, is a high-profile frontrunner, having become the darling of the Conservative Party’s grassroots.

She spent the first two years of Mr Johnson’s premiership as international trade secretary, championing Brexit.

She was appointed Britain’s lead negotiator with the European Union in 2021.

Despite being a big supporter of Mr Johnson over the years, Ms Truss said he was right to step down.

“The PM has made the right decision,” she tweeted on Thursday (Australian time).

“The Government under Boris’s leadership had many achievements – delivering Brexit, vaccines and backing Ukraine. We need calmness and unity now and to keep governing while a new leader is found.”

Photo: UK Parliament

SAJID JAVID

Sajid Javid was the first cabinet minister to resign in light of Mr Johnson’s most recent scandal.

It marked the second time Mr Javid had resigned from Mr Johnson’s cabinet.

Mr Javid, 52, first resigned from the role of chancellor in 2019, a decision driven by his desire to appoint his own staff.

He returned to cabinet in 2020 to serve as Mr Johnson’s finance minister, and most recently served as health minister.

Mr Javid could prove to be a formidable opponent, having finished fourth in the 2019 leadership contest to replace former prime minister Theresa May.

Photo: UK Parliament

PENNY MORDAUNT

Trade secretary and former defence secretary Penny Mordaunt is a quiet contender for the role.

Ms Mordaunt, 49, may earn votes from her fellow party members, who will remember her role in the Johnson government’s Brexit achievement.

Although she previously expressed loyalty to Mr Johnson, Ms Mordaunt was critical of Mr Johnson’s lockdown party scandal, calling the illegal gatherings “shameful”.

Bizarrely, Ms Mordaunt also participated in a now-defunct reality TV diving show ‘Splash!’ in 2014.

Photo: UK Parliament

DOMINIC RAAB

Deputy Prime Minister Dominic Raab will likely join the race for the party’s top spot.

Mr Raab, 48, memorably filled in as the nation’s Prime Minister when Mr Johnson was hospitalised with COVID in April 2020.

But Mr Raab isn’t necessarily a shoo-in for the role. Like Mr Johnson, his past isn’t without controversy.

He was accused along with other Tory MPs of hypocrisy in 2021 when it was revealed they called British workers “lazy” and the “worst idlers in the world” in a co-authored book published in 2012.

As foreign secretary, Mr Raab was heavily criticised for his refusal to cut his holiday short as Afghanistan fell to the Taliban in August 2021.

When will we know who the new leader is?

It could take weeks or even months for the Conservative Party to decide on a new leader. But one is expected to be in place before the Conservative Party’s conference in October.

After former prime minister Theresa May resigned on May 24, 2019, it took almost two months for the party to decide on Mr Johnson as her replacement.

-with AAP