Here are the frontrunners to replace Theresa May as Conservative party leader and prime minister

Johnson is by far the most popular candidate among Conservative members and will probably win a leadership contest if he makes the final two.

According to a recent YouGov poll, 39% of Tory members want Johnson to be the next leader, with second-placed Dominic Raab trailing on 13%.

While there are a sizeable number of MPs who are opposed to Johnson, there appears to be a growing view — even among the moderate wing of the party — that he could be the person to unite the party and rescue its disastrous poll ratings, which have plummeted in recent months.

• Read More: Conservative moderates plan to take back control of Boris Johnson as prime minister

He looks almost certain to make the final two, with the backing of influential MPs from across the party including Johnny Mercer, Jacob Rees-Mogg, and Gavin Williamson.

He would likely claim he is willing to embrace a no-deal Brexit — a policy which is popular with rank-and-file Tory members and probably required for any candidate to win the leadership.

However, a bruising leadership contest could hurt his chances, with his patchy track record in office likely to come under severe scrutiny.

Many colleagues believe he has placed his personal ambition above all principles. As Mayor of London, he championed a liberal, pro-immigration philosophy to a receptive electorate.

When he became MP for Uxbridge & South Ruislip in 2015, he decided to tack right and his been drifting in that direction ever since, a move which has endeared him to the Tory membership, which is typically more right wing than the average Conservative voter.

He last year compared the appearance of Muslim women wearing burkas to "letter-boxes" and refused to apologise.

His decision to back Brexit in 2016 — widely credited as swinging the referendum decisively in Leave's favour — came as a surprise to then-Prime Minister David Cameron, who believed Johnson had made the decision purely on personal ambition.

• Read More: Boris Johnson's long list of gaffes, offensive comments and controversies

Then there is his record as Foreign Secretary.Former colleagues say that he was unwilling to read up on policy documents and he made an extensive series of gaffes which caused international diplomatic incidents. He was condemned for saying the war-torn Libya city of Sirte could be the new Dubai before adding: "all they have to do is clear the dead bodies away."

Raab has the support of up to forty Conservative MPs, including former Brexit minister Suella Braverman, who quit the Brexit department on the same day as Raab last year.

However, he would be a divisive choice for next Conservative leader.

Elected as an MP in 2010, the self-described libertarian is a big hit with the European Research Group of pro-Brexit Conservative MPs and has the advantage of not being part of the Conservative party's tainted old guard.

However, many of the party's moderate MPs believe he is too far to the right, with one party official telling BI that is he is "so right-leaning" and would represent "the complete end of [David] Cameron modernisation."

They believe that he would alienate moderate voters who flocked to the party under the more socially-liberally leadership of Cameron and ex-Chancellor George Osborne.

"We'd never win back the seats we need for a majority like Battersea and Twickenham," the same official said.

"We'd lose Richmond Park in seconds. We'd never win back Canterbury with him in charge. The party would be totally lost and end up in opposition."

• Read more: Conservative Remainers move to back 'least bad' Brexiteer in battle to replace Theresa May

Raab has previously stated:: "I don't support the Human Rights Act and I don't support economic and social rights."

This is why although Labour MPs are uncomfortable about a "hard" Brexiteer Conservative MP like Raab leading the country, the party's leadership believes he'd be very beatable in a general election.

Andrea Leadsom significantly boosted her chances of a successful leadership run on Wednesday when she grabbed headlines by resigning as Leader of the House of Commons in protest at Theresa May's latest Brexit plan.

She made the two-strong shortlist in 2016 — along with one Theresa May — but withdrew from the leadership contest following an embarrassing newspaper interview.

After that, she has become one of the strongest pro-Brexit voices in the prime minister's Cabinet, and unlike many of her ministerial colleagues didn't make any major gaffes.

Friends of Leadsom have told Business Insider that lesser-known Conservative MPs who are planning a leadership bid, like party chairman James Cleverly, have recently asked for her endorsement.

However, Leadsom is strongly considering running again and is being encouraged to do so by allies who are unimpressed by the other Brexit-backing candidates in the running.

For example, one of her backers described pro-Leave leadership frontrunner Dominic Raab as a "psychopath" and "really weird."

One of the issues facing Leadsom is that she is still not taken entirely seriously across the party.

Moderate Conservatie MPs point to her repeated calls for Brexit Withdrawal Agreement to be reopened while she was in Cabinet as evidence she is more interested in rhetoric than policy detail.

Furthermore, the same weaknesses which brought her leadership bid to an early end last time — a CV which has come under scrutiny and Christian views which some say are reactionary — could yet derail a campaign again.

The foreign secretary is an obvious frontrunner and colleagues say he is in the advanced stages of preparing a leadership bid. He has plenty going for him: He survived six years as Health Secretary, a remarkable feat for any minister, and has more Cabinet experience than most of his would-be rivals.

Neither has he embarrassed himself as Foreign Secretary.

However, Hunt campaigned for Remain in 2016, which makes him damaged goods in the eyes of many Tory members. He has since become an enthusiastic Brexit convert, but colleagues say he, along with fellow leadership rival Sajid Javid, has overcompensated on that front, saying that he would prefer a no-deal Brexit to no Brexit at all.

Of Hunt and Javid, one Conservative MP told Business Insider: "The two of them are damaged [...] They supported Remain in 2016. Now, they've now tacked over to the Leave side. But they've overcompensated, and it's not convincing."

The MP said Hunt's criticism of Airbus was an example of such behaviour. The foreign secretary said the aeroplane manufacturer's warnings about the UK's Brexit strategy were "completely inappropriate" and said the government should ignore "siren voices."

"Hunt's attitude to Airbus was absolutely unacceptable. His speech at the party conference was an absolute embarrassment. It's unforgivable, much as I respect him as someone who survived 6 years at health."

Hunt's Cabinet experience could, ultimately, work against him. One Tory MP said they felt the Cabinet ministers who stayed on in government would be too closely associated with Theresa May's disastrous government, and that the next prime minister would be either an outsider or someone who had resigned, like Boris Johnson.

Recently appointed Northern Ireland secretary Rory Stewart has confirmed he wants to be the next prime minister. He has a highly interesting backstory, having previously served in the Army and tutored Prince William and Harry.

He is a very highly rated minister and seen as a modernising force within a party, having spoken about the need to tackle climate change and appeal to younger voters.

However, he is unlikely to win the contest this time round, having campaigned for Remain in 2016 and is not well-known among the wider membership.

Even his enemies do not dispute that Michael Gove is a highly effective minister who has been successful at driving through major policy achievements, particularly during his time as Education Secretary and presently as Environment Secretary.

His leadership bid also has the backing of influential colleagues, including Ed Vaizey, Tom Tugendhat, and Mel Stride.

Michael Gove has one enormous problem though: He is deeply unpopular with Conservative members, as well as with the wider public. Just 12% of British voters have a positive opinion of him, according to YouGov, and 52% have a negative opinion.

His decision to "knife" Boris Johnson in 2016 — he announced that Boris was unfit to become leader despite running his leadership campaign at the time — and run for the leadership himself has created the perception of a self-interested politician without principles.

And while he is a committed Brexiteer, his loyalty to Theresa May means he is seen as the wrong kind of Leaver; one who is closely associated with the prime minister's hated Brexit plan, having come out to bat for it in parliament on multiple occasions.

He is unlikely to be the next leader.

The newly installed Home Secretary would be a dark horse to take over as the next leader, and she is understood to be considering a run.

She is well-respected by many colleagues, she voted Leave, and her reservations about Theresa May's deeply unpopular Brexit plan have been made known, although she didn't resign from Cabinet like other Brexiteer colleagues.

She has relatively few enemies — an important quality in any leadership race — and her relatively low-profile is likely to grow significantly if she does choose to run.

She doesn't have the same backing from colleagues as other Brexiteers who are planning to run, however, which may discourage the Home Secretary from putting her name forward.

Home Secretary Sajid Javid will pitch himself as the politician who can unite the Tory party and sell it to the nation with a brand of free-market Toryism that has much in common with Thatcherism.

He has an interesting backstory as the son of a Pakistani bus driver which could sell well to voters and improve the party's image as lacking in diversity.

He has often made headlines as Home Secretary — not all of them positive — but critics say he has not got enough to show in terms of policy achievements during his five years in Cabinet across four different briefs. He is also accused of lacking a political identity by some, having wavered between pitching himself as a liberal, pro-immigration Tory and a hardliner.

His nascent campaign team is being run by Matthew Elliott, who successfully ran the Vote Leave campaign. He is the first choice of 9% of Tory members currently.

Liz Truss — who is expected to run in the forthcoming leadership contest — is on the rise, and many of her colleagues believe she will go further than expected in the race.

She is a Brexiteer, she has done well in her Treasury post — where she is second in command to Chancellor Philip Hammond — and she has made the sort of noises about Britain's readiness for a no-deal Brexit which will endear her to the Tory membership, many of whom support such an outcome.

She has also carved a niche for herself as a champion of free market Toryism, a neat contrast to the more paternalistic Theresa May. It also means she has achieved the rare feat of being able to talk about something other than Brexit since the EU referendum, something which many of her colleagues believe is a vital quality.

As one former Cabinet minister told Business Insider: "Brexit will dominate our politics for the next five years at least. But we need a leader who's capable of talking about more than that.

"Liz — while I don't necessarily think she will be leader — has developed a real niche as a champion of free markets. People didn't take it seriously when she started doing it but they respect her now. We need more MPs like that."

Others believe she comes across as a bit too much of an oddball to make it all the way, pointing to a now notorious speech in which she vented her fury at the amount of imported cheese in the UK. "People like Liz but she does come across as a bit weird. That cheese speech will come back to haunt her."