Conservative leadership candidates are in talks about joining forces to provide the strongest challenge to Boris Johnson, who looks all but certain to be Britain’s next prime minister after trouncing rivals in the first MPs’ ballot.

Johnson hoovered up the votes of 114 MPs, more than a third of the parliamentary Tory party, and enough backers to guarantee him a place in the final two, assuming he retains their support in later rounds.

His closest rival, the foreign secretary, Jeremy Hunt, was trailing in a distant second place, with 43 votes. Johnson thanked colleagues and insisted “We have a long way to go”, but MPs believe it would take an extraordinary upset to halt his passage to No 10.

Boris Johnson (@BorisJohnson) Thank you to my friends and colleagues in the Conservative & Unionist Party for your support. I am delighted to win the first ballot, but we have a long way to go.https://t.co/tGRXu94CmT | @BackBoris pic.twitter.com/zVBNls2rew

Conservative MPs, including the prime minister and all 10 candidates, cast their votes in a wood-panelled committee room of the House of Commons on Thursday morning.

Three candidates, Andrea Leadsom, Mark Harper and Esther McVey, were automatically eliminated after failing to reach the threshold of 17 votes required to proceed to the next round.

Among the seven remaining, the health secretary, Matt Hancock, was facing pressure to withdraw from the race and throw in his lot with another contender. He had hoped to poach supporters from Rory Stewart, but Stewart insists he is determined to go forward after securing 19 votes to Hancock’s 20.

Members of the health secretary’s team have privately spoken to advisers from both Michael Gove and Sajid Javid’s camps to discuss a possible alliance. A decision on “consolidation” is expected imminently.

Candidates who want to drop out before the next round of voting next Tuesday have been asked to tell the 1922 Committee of their decision by lunchtime on Friday.

One campaign source said they believed Gove was the more likely beneficiary of Hancock’s support, as the candidate with the best chance of getting to the final two with their backing, but said that Javid had made a strong pitch that he was the most plausible change candidate, with a sufficiently different pitch to Johnson, looking and sounding “more like the future”.

But another Hancock supporter said it was becoming clear that more moderate candidates needed to unite to properly challenge those supporting a hard Brexit. They added: “That’s the conversation going on: could Matt and Saj combine?” Hancock and Javid held a face-to-face meeting on Thursday afternoon to discuss the way forward, but no agreement was reached.

Many of Hancock’s supporters are understood to have little enthusiasm for a deal with Hunt, seeing him as the continuity candidate with support mainly from the party establishment. They also believe it would be humiliating to do any deal with Stewart.

Johnson is running a carefully managed campaign, and has been accused of avoiding close scrutiny in the contest.

Late on Thursday it was announced that all the other six candidates had committed to appear in televised leadership debates on Sunday and Tuesday, piling pressure on Johnson.

In a joint statement, Hunt, Gove, Javid, Hancock, Stewart and Dominic Raab said: “The next Conservative leader, and prime minister, will have the crucial task of uniting Britain behind a new vision - not only to deliver Brexit, but to define what comes next.

“This leadership contest provides an important opportunity to debate, to shape and to define the ideas which will underpin those competing visions. That is why we are committed to taking part in the Channel 4 televised debates this Sunday and the BBC programme next Tuesday.”

Johnson’s spokesman has said he was “in discussions” with broadcasters.

Earlier, the former Brexit secretary David Davis, who is backing his successor and one-time chief of staff Raab, said: “All the candidates should take part in the debates. The more you are clear about your policy, the stronger your mandate when you start as prime minister. The debates matter. I did five against David Cameron. Then the public know what you stand for – that’s quite important.”

Moderate Tories have become increasingly alarmed about the risks of a Johnson premiership. The former foreign secretary has secured the backing of the most Eurosceptic MPs after promising to deliver Brexit on 31 October, with or without a deal.

The chancellor, Philip Hammond, who has not yet endorsed a candidate, wrote a public letter to all seven on Thursday, urging them to commit to continue reducing the national debt every year, and to keep the deficit below 2% of GDP.

“The Conservative party has a hard-won reputation for fiscal and economic competence that has been the bedrock of our electoral success over generations. As we enter the campaign to select our next leader, it is vital that we do not throw that away,” he said.

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He said that would still allow modest increases in spending, but that if the Tories failed to keep tight control of the public finances, they would be unable to “demonstrate a dividing line between the fiscal responsibility of our party and the reckless promises of John McDonnell and Jeremy Corbyn”.

The chancellor’s remarks were widely read as directed at Johnson, who has promised to spend £10bn on a tax cut for higher earners. Raab has also made lavish spending pledges, including a 5p cut in the basic rate of income tax.

Another ballot of MPs will now be held next Tuesday, with further rounds to follow on Wednesday and possibly Thursday, until the field is narrowed to two. Their names will then be presented to Conservative members in a postal ballot, with the winner due to be announced in the week of 21 July.

The new prime minister will then have just three months to prepare for Brexit by the Halloween deadline set by EU27 leaders.

Candidates will need at least 33 votes to proceed into the third round. Conservative party HQ announced on Friday that they would be allowed to spend a total of £150,000 over the course of the campaign, starting on 7 June.