Contenders in the race to replace Theresa May as prime minister are vying to claim the mantle of the “stop Boris” candidate, after the former foreign secretary scored an emphatic victory in the first round of voting.

With Boris Johnson all but guaranteed a place on the shortlist of two from which Conservative members will pick a new leader, the contest is focused on whether the second slot will go to someone with a realistic chance of keeping him out of 10 Downing Street.

Rival camps believe that Mr Johnson would privately welcome a run-off ballot with the formerly Remain-backing Jeremy Hunt, who took second place in the first ballot, because he would be seen by activists as a “continuity May” candidate who risked a repeat of the current prime minister’s EU stalemate. Some suspect he may even “lend” some loyal supporters to the foreign secretary to consolidate his position in the second round on Tuesday.

Outsider Rory Stewart staked a dramatic claim as Johnson’s fiercest opponent, vowing to call a rival parliament to sit outside the Palace of Westminster and “bring him down” if he tries to force through a no-deal Brexit by locking the doors to MPs.

But Sajid Javid’s team said that private polling showed the home secretary was the candidate best placed to provide a real alternative to Mr Johnson, and that his inclusion in the final ballot would offer “a clear choice between two types of change”.

Who is standing to be the next prime minister? Show all 3 1 /3 Who is standing to be the next prime minister? Who is standing to be the next prime minister? Boris Johnson - 157 votes Foreign Secretary Boris Johnson arriving in Downing Street, London, for a Cabinet meeting where Theresa May will brief on her plans for Brexit before a major speech aimed at helping to break the deadlock in the negotiations with Brussels. PA Who is standing to be the next prime minister? Michael Gove - 61 votes LONDON, ENGLAND - JUNE 07: Britain's Environment Secretary Michael Gove leaves 10 Downing Street on June 7, 2018 in London, England. Prime Minister Theresa May is holding an emergency Brexit cabinet meeting in an attempt to resolve tensions over the UK's Irish border plan. (Photo by Simon Dawson/Getty Images) Getty Who is standing to be the next prime minister? Jeremy Hunt - 59 votes Health and Social Care Secretary Jeremy Hunt leaving Downing Street, London, after attending a Cabinet meeting. PA

Former prime minister Sir John Major said the prospect of a new head of government using the process of “prorogation” to suspend parliament in order to stop MPs blocking a no-deal Brexit was “not only fundamentally distasteful, it is hypocrisy on a gold-plated stand”.

And veteran former cabinet minister Kenneth Clarke said anyone using this tactic – which has not been ruled out by Mr Johnson or Brexit hardliner Dominic Raab – would effectively “rule themselves out” as being fit to be prime minister.

Meanwhile, the chancellor, Philip Hammond, issued a warning to candidates not to make reckless spending pledges in the battle for votes. In a letter to all remaining contenders, Mr Hammond asked them to commit to keeping the national debt falling every year and limiting the deficit to 2 per cent of GDP to 2021-22.

Writing after Mr Johnson promised to spend part of the chancellor’s no-deal war chest on a tax break for high earners, and Michael Gove offered to scrap VAT, Mr Hammond said: “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.”

Despite whispers that Mr Johnson’s campaign chair Gavin Williamson is pressing fringe candidates to help bring the contest to an early close by dropping their bids, few in Westminster expect withdrawals ahead of the next round of voting – not least because of the prospect of a televised debate on Sunday.

Rival camps were putting pressure on Mr Johnson to take part in the 90-minute Channel 4 broadcast, which they see as an opportunity to assault chinks in the armour of the frontrunner, who has so far largely avoided scrutiny.

Mr Gove pointedly said he looked forward to seeing “all other candidates” there, while a source in Mr Javid’s camp said: “The Tory party mustn’t be deciding the next prime minister behind closed doors.”

Sources close to Mr Johnson said he was still “in discussions” with Channel 4 over his participation. If he pulls out, it is expected that Mr Hunt will do the same, leaving the two frontrunners to be empty-chaired in a five-way debate.

A Hunt confidante said he was “actively preparing” for the TV showdown, but he is committed to attend only if all the others do likewise. Johnson ally Andrew Mitchell said there was “no reason” for the former foreign secretary to debate a wide field of rivals when he has already established such a dominant position.

Mr Hunt scooped 43 votes and Mr Gove 37 in the first MPs’ ballot, which saw Mr Johnson claim a commanding 114 and Andrea Leadsom, Mark Harper and Esther McVey eliminated after amassing just 11, 10 and nine votes respectively.

The battle is on to win over their supporters, with Mr Johnson thought to be in pole position to claim backers of the Eurosceptic Ms Leadsom and Ms McVey.

With 19 votes in the first round, Mr Stewart faces an uphill struggle to reach the threshold of 33 on Tuesday, as do Matt Hancock, the health secretary, on 20, Mr Javid on 23 and Dominic Raab on 27.

But David Gauke, the justice secretary, said Mr Stewart was “potentially the biggest threat to Boris Johnson” after a straw poll of readers of the ConservativeHome website suggested the international development secretary was the second-favourite choice of activists.

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Mr Javid’s team released private polling which they said bolstered his claim to be the “new generation candidate”.

The YouGov survey, conducted between 5 and 10 June before his campaign launch, found the home secretary leading the four frontrunners as best able to unite Remainers and Leavers in the party, to relate to the challenges facing ordinary people and make progress with ethnic and youth voters.

A campaign spokesman said: “Today’s results show a clear appetite for a fresh face and new ideas at the top of the Tory party. It’s vital that the party’s final contest is a real contest that reflects modern Britain.”

The Conservative Party chair, Brandon Lewis, and the acting co-chairs of the Tory backbench 1922 Committee announced that the first members’ hustings will take place in Birmingham on 22 June between the two candidates who emerge victorious from the successive rounds of MPs’ votes next week.