National's caucus is heading for a showdown today between leader Simon Bridges and MP Jami-Lee Ross.

Ross is on medical leave from Parliament and it is not yet known whether he will face his colleagues in caucus today as they discuss his future.

It hangs in the balance after he was named as the person who leaked details of Bridges' expenses to the media in August. He also sent out a series of tweets accusing Bridges of unlawful behaviour, among other things.

The episode is also casting a shadow on Bridges' leadership but National MPs were yesterday backing him.

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Ross came out swinging yesterday, issuing a series of tweets even before Bridges named him as the leaker which said Bridges was trying to pin the blame on him.

"Some months ago I fell out with Simon. I have internally been questioning leadership decisions he was making, and his personal poll ratings which show he is becoming more and more unlikeable in the public's eyes.

"When I started to become expendable, I confronted him with evidence that I had recorded him discussing with me unlawful activity that he was involved in. Working on his instruction, he asked me to do things with election donations that broke the law.

"This evidence led Simon to push me out on medical leave a few weeks ago. It was essentially an attempt to stop me from speaking publicly," Ross said.

Bridges yesterday categorically denied any allegation of wrongdoing on his part, telling Newstalk ZB's Barry Soper Ross' allegations were the "sort of thing he would say. I'm not surprised, frankly."

National leader Simon Bridges and deputy Paula Bennett front media yesterday on Jami-Lee Ross. Photo / Doug Sherring
National leader Simon Bridges and deputy Paula Bennett front media yesterday on Jami-Lee Ross. Photo / Doug Sherring

Bridges said he and deputy leader Paula Bennett visited Ross yesterday to confront him with report's findings.

He was not satisfied with Ross' explanation, or by other matters about his conduct which Bridges said suggested a pattern of behaviour.

Bridges said he "would never" break the law.

"We've got someone lashing out, an MP on their own who now has these reports in relation to their activity. I think the only interesting thing there is he's confirming he's taping colleagues."

Bridges also rejected Ross' that he was forced out on medical leave in an attempt to gag him.

"I took Jami-Lee Ross at his word in relation to the health issues and today I balanced those against the very clear public interest in this leak report," he told Soper.

Bridges admitted earlier yesterday that an error had been made in relation to two donations totalling $24,000 which were recorded as donations for him instead of the party.

"There has been nothing inappropriate there. It was a mistake," he told Newshub, adding that it was corrected "very quickly" after National received advice from the Electoral Commission.

The PwC report commissioned by National, which looked at phone and computer records of National MPs, said it had not identified with certainty the leaker of the expenses nor the person who later sent a text regarding the leak. But it said the evidence pointed at Ross.

Senior National MP Judith Collins said the PwC report "speaks for itself" and slammed Ross' tweets.

"What's been said today on Twitter is pretty appalling. I would not put up with it if I was in [Bridges'] position."

Fellow National MP Maggie Barry was even more scathing, tweeting "What a disloyal disgrace this flawed & isolated individual has become. Having now read the PwC report I personally believe the unpleasant & bullying pattern of behaviour of Jami Lee Ross has no place in an otherwise united National Caucus under our leader Simon Bridges."

If the 55-strong caucus (excluding Ross) vote to suspend Ross, he could stay on as an independent MP or force a byelection in his electorate of Botany.

It would be up to the National Party board to determine whether he would be suspended or expelled from the party.