Sir Roger Gale has branded Boris Johnson a "conference clown" who is unfit to be the next Prime Minister.
The Conservative MP told talkRADIO's Mike Graham that the ability to "make people laugh" was not a desirable quality in the next inhabitant of Number 10
"Mr Johnson is regarded as the conference clown, the darling of the warm-up, the person who makes people laugh," he said.
"That's not what you're looking for in a Prime Minister, particularly not what you're looking for in a Prime Minister at one of the most serious times in our nation's history."
Sir Roger is backing Jeremy Hunt in the leadership race, who is set to face his rival Mr Johnson tonight in a debate hosted by talkRADIO and The Sun.
"I was at a hustings last week in Maidstone and it was actually no contest," Sir Roger recounted.
"You saw people going in saying 'I think we're backing Boris' and coming out saying 'We're not'."
He continued: "There's a popular belief that most of the ballot papers are already in so it doesn't make any difference. But the fact of the matter is, most of the ballot papers are not already in. People are waiting to hear the hustings on the media and in person, and then making up their minds."
According to Sir Roger, Mr Hunt has won support for his belief in securing a deal with Brussels, whereas Mr Johnson has refused to rule out suspending Parliament to push through a no-deal Brexit.
"It looks as though what Mr Johnson will do is waste two months and then say, 'Well, we've got to get out on October 31 and that's it. Hard Brexit. Finish," he added.