With Boris Johnson having locked down a place in the final two of the UK Conservative's leadership race, barring a disastrous mistake over the next two days, the focus is shifting to finding a credible challenger in phase two of the contest, when party members choose from the two top candidates.

On Wednesday, MPs will vote in the third round of the contest's first phase which, in a change to the threshold rules in the opening rounds, will see the final five surviving candidates battling to avoid receiving the fewest number of votes.

In round two on Tuesday, hardline Brexiteer Dominic Raab (30 votes) was eliminated after failing to hit a 33-vote threshold, and Johnson added another 12 supporters to his first round tally to take a clear lead on 126 of the 313 Conservative MPs.

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The key battle now lies in the fight between four closely-matched surviving candidates: Foreign Secretary Jeremy Hunt (46 votes in round two, up three), Environment Secretary Michael Gove (41 votes, up four), International Development Secretary Rory Stewart (37 votes, up 18) and Home Secretary Sajid Javid (33 votes, up 10). 

Supporters of the four are under pressure to decide whether to rally behind a single candidate to take on Johnson, continue voting for their candidate, or back the frontrunner.

A live BBC debate, the first Johnson has agreed to take part in, did little to clarify matters on Tuesday evening, as the five remaining candidates took to national television to appeal to their colleagues in parliament.

Hunt, Gove and Javid have a similar approach to Brexit. All are willing to take Britain out of the European Union without a deal if a breakthrough isn't found in negotiations by October 31.

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Stewart is the odd man out, arguing that his rivals' stance is unrealistic and saying he would not oversee a no-deal exit. He has the momentum among the four, up 19 votes since the first round but has also become a target as the fight for second place intensifies. 

He was repeatedly attacked in Tuesday evening's TV debate, while frontrunner Johnson had an easier ride from fellow candidates.

Stewart appeals to moderates in the party, but his approach on Brexit is unlikely to be a hit with members. New polling from YouGov indicates Brexit is more important to a majority of them than keeping the United Kingdom or the Conservative Party together. 

Javid and Stewart are the most vulnerable in the next round, with neither expected to pick up many of Raab's 30 votes. The eliminated Brexit hardliner's support is most likely to head to the two candidates who voted "Leave" in the 2016 referendum, Johnson and Gove.

That probably leaves Javid and Stewart fighting to maintain their current support and hoping for a collapse in backing for second-placed Hunt, though there has been no sign of MPs deserting the foreign secretary.

There may also be a temptation among Johnson's campaign to lend support to Javid to knock out Stewart, the strongest critic of the frontrunner, and limit momentum for Gove, who brought down the former London mayor's leadership bid in 2016 and claims to be the purist Brexit voice among the candidates.