Christopher Luxon not ruling out National Party leadership tilt as Judith Collins refuses to confirm caucus purge after Todd Muller resignation

Judith Collins is refusing to say whether she's purging leakers from her caucus after Todd Muller was forced to resign for backstabbing a fellow National MP to the media.

Collins' MPs seem to have got the message for now but leadership hopeful Christopher Luxon still isn't ruling out a tilt at her job.

Leaks from National's caucus have been cauterised, made clear by effectively ousting Muller for leaking. 

"I don't think leaking is the right thing to do and the leader has made that clear," former leader Simon Bridges said on Tuesday. 

But Collins won't say if she's purging the leakers. 

"I'm focused on the things that matter."

Collins has sent the mother of all warning shots to her caucus to focus. 

"I'm making that very clear," she said on Tuesday. "When you talk about things like leaks in caucus, those are matters for me to deal with."

But Collins doesn't view her leadership as becoming more ruthless. 

"Oh, I think that's such a harsh term."

Last week Collins called a late night caucus meeting. She won't say if she gave Muller an ultimatum to resign or be booted from caucus. 

"Well I can't possibly do that, can I?"

Muller backstabbed returned MP Harete Hipango to media over whether she used taxpayer money to buy furniture.

The newly returned National MP wouldn't be drawn on the issue on Tuesday. 

"I'll just say that it's good to be back," she said. "We're going to move on with that, as I say the matter's been dealt with appropriately by Parliamentary Services."

In an apparent case of amateur hour, Muller reportedly did his trash talking of Hipango in front of another MP - Barbara Kuriger. But Kuriger also wouldn't confirm what happened. 

"It's a caucus matter. It's a matter for caucus and that's all I have to say, thank you," Kuriger said as she walked off. 

Collins' handling of Muller has been savaged by her former chief press secretary Janet Wilson, who has called it "paranoid head-rolling".

But Collins laughs in the face of paranoia.

"What do you think?" she laughed. "Of course not."

Though she may have good reason to be paranoid. Leadership hopeful Christopher Luxon, the former CEO of Air New Zealand, is still very hopeful. 

"Judith's doing an amazing job, she's doing an awesome job, I'm fully supportive of her, I found her very good to work with," he said on Tuesday. 

But he wouldn't rule out a tilt at the leadership. 

"I'll be honest, I've come in new, I've got lots to learn."

This is Collins' most cutthroat attempt at putting an end to National's seemingly endless exercise in self-destruction.

The problem for her is Muller wasn't the first National MP to speak out of school, nor will he be the last.