Contenders to be Britain’s next prime minister have lined up to dismiss calls for an unchallenged “coronation” of Boris Johnson, as the Tory leadership race turned increasingly bitter ahead of a second round of voting.

It comes as all six of the candidates vying for the keys to No 10 appeared on stage at a hustings session hosted by the National Conservative Convention – an event originally scheduled for a vote of confidence in Theresa May.

Reports had suggested senior party figures were hoping to avoid weeks of “blue on blue” attacks, and instead were drawing up plans for the other candidates to withdraw after the former foreign secretary gained an overwhelming win the first ballot of MPs.

This would result in Mr Johnson’s name alone being put forward to a confirmatory vote of members, essentially making his election as Tory leader a formality.

But the home secretary Sajid Javid, the foreign secretary Jeremy Hunt, the former Brexit secretary Dominic Raab and the international development secretary Rory Stewart all strongly condemned the plan.

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

In his pitch to Tory members, Mr Javid said a coronation of Mr Johnson should be avoided as he joked “that worked well last time” – in reference to the 2016 leadership contest when Andrea Leadsom dropped out of the final two, resulting in Ms May being crowned leader.

“The party and the country deserve a good choice,” Mr Javid told reporters outside the hustings event. “There needs to be a proper process that’s followed through. Let’s give the opportunity to the members to have their say.”

Mr Stewart echoed his cabinet colleague’s remarks, saying: “The members of the Conservative Party who are wise, sensible, experienced people, deserve to have a choice.

“We should have learned from the last time round that coronations are not the way to do democratic politics.”

Mr Raab also insisted on the need for “proper scrutiny” in the contest, claiming the longer the process goes, “the more the underdog gets their shot”. Mr Johnson had avoided reporters as his Range Rover pulled up at a side door at the London hotel where the event was being held.

On Saturday, the former London mayor also faced fresh mockery for his decision not to participate in a televised debated hosted by Channel 4 tomorrow evening. The broadcaster intends to present viewers with an empty podium for the former foreign secretary.

“If you can’t take the heat of the TV studios what chance of taking the heat of the negotiating chamber in Brussels?,” his rival Mr Raab told The Daily Telegraph.

Jeremy Hunt-backer Amber Rudd, who stood in for Ms May in the 2017 general election televised debates, also joked: “If Boris doesn’t want to do Sunday, I’m very much available to step in for him.”

The remaining six candidates in the Conservative leadership contest, clockwise from top left: Michael Gove, Boris Johnson, Dominic Raab, Sajid Javid, Jeremy Hunt and Rory Stewart (AFP)

Mr Johnson has agreed to appear in the second debate on Tuesday – hosted by the BBC – after at least one contender is eliminated in a second round of voting by MPs earlier that day. Voting will continue until Thursday at the latest, when just two final candidates remain.

Five of the six candidates, who have pledged to remove or alter the Irish backstop in further round of negotiations with the EU, were also dealt a fresh blow at the weekend as the Irish prime minister Leo Varadkar said removing the insurance policy would be represent the same threat as a no-deal Brexit.