A former adviser to Todd Muller during his brief tenure as National Party leader has revealed secrets from behind the blue curtain.

Political commentator Matthew Hooton was an early advocate for Muller to roll Bridges, after a dire Colmar Brunton poll in May showed the party down on 30 per cent support. 

Muller succeeded in his coup, but his tenure lasted only 53 days before he stepped down for mental health reasons, paving the way for Judith Collins to take over.

However, the low poll numbers have not recover, with the latest Colmar Brunton poll putting National just one point higher than the May poll - on 31 per cent, trailing behind Labour's 48 per cent.

Hooton, who took on an advisory role with Muller, told Heather du Plessis-Allan he does not regret backing Muller. He says that it was necessary to replace Bridges, as the private polling was worse than the public polling.

"Bridges was literally the most unpopular senior political figure in the English-speaking world. Public decided they did not want him to be Prime Minister."

Those private poll results were as low as 26 per cent, Hooton revealed, and that the leadership team of Muller and Nikki Kaye were stunned when they took over. 

Muller was the only possible candidate in May, Hooton says. He revealed that Collins and Muller attempted to roll Bridges in April 2019, with Collins as a leader and Muller as deputy, but they couldn't get the numbers.

Hooton served as an adviser for Muller, describing it as being a "chief friend". Despite that, Hooton was not aware of Muller's deteriorating mental health as leader.

He says Muller began having panic attacks within days of becoming the Party's new leader, but he didn't tell Hooton or the party's chief of staff.

"And he could have said he had these panic attacks, what the hell do I do, and we would have seen him off to his GP, and a week of prozac and he'd be better."

When Collins took over, there was an offer for him to stay, but Hooton says that it was like being a spare prick at a wedding. 

He denies, though, that there was any frostiness between them. In fact, Hooton says that Collins is the right person for the job, and Bridges should have never been in the job. 

"She should have become leader when [Bill] English stood down. She even possibly should have become Prime Minister when [John] Key stood down," as it would have led to more rejuvenation. 

Hooton suggests that gender is one of the reasons why Collins wasn't promoted earlier, but the debate last night shows that she is the best candidate for National of the three leaders from this year. 

However, Hooton says National's secret polling shows there's a segment of the population who loves Jacinda Ardern so much -- that if Judith Collins were to lay in to her too hard, even National supporters won't vote blue.

"If they criticise Ardern too harshly, they will actually go down. There are other people who want her to get stuck into Ardern, but there are good reasons not to."