Sunak admitted he was the underdog in the battle for leadership but said he would fight for every vote.
And he was confronted by a party member in the audience who told him that many people thought he had been “treacherous” to Boris Johnson and “stabbed him in the back”.
Mr Sunak replied that: resign was the right thing to do – and that he would be able to bring the party together.
‘Better secondary schools’
When asked by host Nick Ferrari if he would bring back grammar schools, the former Chancellor said: “Yes, as you’ve heard from me before, I believe in teaching excellence. I believe education is the most powerful way to change people’s lives. .
“But I also believe we can do a lot in the school system as it is. It’s about reforming the system to get better grammars.”
Mr Sunak’s team later clarified that the comment was “about expanding existing high schools”.
Grammar schools were an important part of the post-war educational scheme, with children across the country taking the eleven-plus to decide whether to be admitted or attend the local secondary modern school instead.
But in the 1960s and 1970s, most parts of the country decided to go inclusive, meaning children with different abilities all went to the same school.
In 1998, Labor ruled that public secondary schools could not be opened, and existing schools were banned from introducing new aptitude-based selection.
It means there are now only about 160 grammar schools in England. Mr Sunak’s promise to return to selection could therefore herald a revolution in the English education system.
‘You stabbed him in the back’
Matthew Dransfield, a 47-year-old business investment adviser from West Yorkshire, challenged Rishi Sunak to stab Boris Johnson in the back.
He said during the live show: “Rishi Sunak, you are a good salesman and you have many strong qualities, but many people continue to support Boris Johnson, who has consistently delivered through treacherous waters.
“A lot of people unfortunately think you stabbed him in the back. Some people don’t want to see that in number 10.
‘I don’t know exactly what planet you’re on. How do you expect to see the party through the next elections?’
Mr Sunak replied that he was “very grateful to the Prime Minister…I gave my all to that job”.
“For me personally, it got to a point where I couldn’t stay. I had a significant difference of opinion with him on how to deal with the economic challenges ahead.
“And with a situation like that, I absolutely couldn’t stay. I had no choice but to resign and I’m sad I had to, but that was the right thing to do and that was that I acted on my principles.”
He said he resigned “because the prime minister and chancellor cannot sit in another place when it comes to economic policy”.
After the looting, Mr Dransfield said the Prime Minister had been the victim of “a coup” and MPs “had a very short memory and could not remember the success Boris Johnson had delivered in very difficult times”.
“In the end he was stabbed in the back by some MPs and this is what we’re looking at and it’s a bit unreal,” he said.
Dransfield, who said he would not vote for Sunak but might support Ms Truss, said he still hoped the prime minister’s name would be added to the contest.
Revealing that he had signed a petition calling for Mr Johnson’s reinstatement, he said: “A lot of the Commons don’t understand that we shouldn’t be holding this stupid contest.
“It is not a good thing for this country at a time when we are facing huge problems around the energy crisis, the war.
“I hope Boris might get back in the mood,” he said, describing the prime minister as “a lot better than” the two candidates in the race.
He said that Mr Sunak’s role in the prime minister’s downfall should effectively exclude him from the leadership, adding: “I don’t think it is possible to overcome this act that he has committed.
“I think it’s insidious. It’s a terrible thing to do and it’s not good for the country right now. Boris Johnson took a landslide victory.
“He has brought about something the way I see it. Of course there are some politicians who felt compromised, but this herd movement, it’s terrible.”