Boris Johnson is under pressure to debate in Tory leadership hustings, as criticism of his near blackout on public speaking grows.
The frontrunner has so far taken just six questions from journalists in his highly stage-managed campaign, and has been refusing media requests for interviews.
As he opened up a considerable lead, pulling 71 votes ahead of his six rivals, one demanded to know “what have you got to hide?”.
Mr Johnson’s opponents have ganged up by committing to appear on TV leadership debates on Sunday and Tuesday, where Channel 4 has said he will be represented by an empty chair if he refuses to take part.
Mr Johnson’s spokesman has said his client is “in discussions” with broadcasters.
In a joint statement, Jeremy Hunt, Michael Gove, Dominic Raab, Sajid Javid, Matt Hancock, and Rory Stewart said the leadership contest was “a critical moment” for both the UK and the Conservative party.
They 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.”
Those campaigning against Mr Johnson warned his strategy of avoiding media scrutiny could land the Tories with the same sort of leadership coronation that delivered victory for Theresa May without her being stress-tested under the spotlight.
A campaign spokesman for Mr Stewart added the next leader must demonstrate they have the capability to “win back old voters and win over new audiences”.
He added: “Any candidate who seeks that mantle can hardly opt out of a public debate.
“If any candidate ducks that duty, there is a simple question we should ask: ‘What have you got to hide?'”
Meanwhile, Mr Raab – who is seeking hard Brexit votes like Mr Johnson – also called for a “proper debate”.
He said: “I’m looking forward to the first televised debates on Sunday and I hope that everyone gets involved – we should have a proper debate on the vision for the country.”
Meanwhile, Mr Hancock is understood to be considering pulling out of the race to support another candidate with a better chance of winning the 33 votes needed to get past the next round.
The Times reported the Health Secretary met Mr Javid, the Home Secretary, but th emeeting appears not to have resulted in any agreement and Mr Hancock is now thought to be more likely to back Mr Gove or Mr Hunt.
Amber Rudd, the Work and Pensions Secretary, told Mr Johnson it was his duty to debate with his rivals and “get out and do the TV debates”, according to the Times.
There are calls for the four candidates at the bottom of the results table to drop out and speed up the process of selecting the next leader.
One of Mr Johnson’s supporters labelled the four “vanity candidates”, the Telegraph reported, saying only Mr Johnson, Mr Hunt and Mr Gove should stay in the race.
They added: “Anyone else who tries to carry on is being indulgent.”
If there were only three candidates left by next Tuesday’s vote, one would be eliminated and the contest could proceed to the next stage of voting by the party membership the same day, instead of next Thursday as currently scheduled.