National Party leader Simon Bridges says police have identified the person who sent him a "dark and concerning" text message claiming to be the leaker of his expenses.
Bridges said he has been "very worried" about the health of the person, who police have spoken to.
The National leader said he received the "dark and concerning" text message on Thursday and it was sent also to Parliament's Speaker Trevor Mallard and a media organisation.
"The text made clear to me that it was from the leaker ... [and that] the leaker was in the National caucus," Bridges told media this morning.
"It also made quite clear that this person had a long and serious mental health issue.
"It was my very clear view there would be significant harm to them if the investigation proceeded. It was a dark and concerning text message.
"I was very worried about it. I spoke to senior colleagues and then replied, saying my utmost concern was for the welfare of the person. Later that day I received expert advice on how to proceed.
"On Friday I informed the police with my clear concern being for the mental health and wellbeing of the individual.
"On Sunday evening police contacted me. They knew and had worked out the identity of the person concerned. They made clear the person was getting the help they needed."
Bridges said police had not told him the person's identity and he understood why this was the case.
The texter had claimed to be inside the National Party and had leaked Bridges' expenses to punish him for being arrogant.
Bridges said he has not questioned members of his caucus about whether they sent the text.
Bridges says he believed he has the support of his colleagues and his main concern was for the wellbeing of the person who sent the text.
"I can't think who it is ... I feel strong support. Whether it's a National MP ... I hope we can find out."
He said it was important to get to the bottom of who leaked the material in order to protect the integrity of Parliament.
Bridges said the person who sent the text clearly knew his mobile phone number and Mallard's.
He said he would not release the text to the public.
Bridges was flanked by senior MPs Amy Adams, Mark Mitchell, Gerry Brownlee and Todd McClay at the media conference.
In a statement, polices said confirmed they met Bridges on Friday over concerns for the welfare of an individual.
"Police assessed the information supplied as a mental health issue requiring an immediate response.
"The information provided by the National Party did not identify the individual, however their identity was established through subsequent police enquiries. Steps were taken, as they are for any matter reported to police, where there are immediate concerns for the welfare of an individual," the statement said.
"Police have dealt with this matter entirely from a mental health perspective."
Any requests for information from the inquiry would be considered on the basis of privacy principles, and police may seek advice as required regarding such requests.
Texter claimed to be National Party member
Bridges and Speaker Mallard both received an anonymous text message last week from a person claiming to be responsible for leaking the information to Newshub, RNZ reported earlier today.
It's understood a conference call involving the caucus has also been held this morning.
The text author reportedly said they had leaked the expenses because they disagreed with Bridges' leadership style, describing him as "arrogant", and wanted him to be held to account for his spending of taxpayers' money.
The author of the text warned they had suffered from mental health problems in the past and said being exposed publicly could push them over the edge and put their life at risk.
The appeal came after Mallard launched an inquiry into who leaked the expenses and promised to name and shame the person responsible.
Sources say the text was extensive, and was sent from an anonymous number.
Police have also become involved and National sought advice from mental health experts on how to deal with the text.
Mallard told the Herald this morning he will be making no comment on anything to do with the incident or the inquiry until the terms of reference are prepared: "end of story".
A request for comment after Bridges' press conference was also declined.
Newstalk ZB political editor Barry Soper has told Mike Hosking Breakfast that he understands it isn't a National Party MP.
"It could be anyone with a burner phone," Soper said.
"To me it's a storm in a teacup.
"Some National MPs are on their way to Wellington today, but not for a spill. It's a show of support for Bridges for when he speaks to the media this morning.
"It was quite a detailed text but, as I understand it at this stage, it isn't a National MP – but we'll have to wait and see."
RNZ said it had not seen the text, which is believed to have detailed a number of conversations and pieces of information from National caucus meetings over a period of weeks in an attempt to prove the author was a National MP.
Mallard has appointed former solicitor-general Michael Heron QC to investigate the leak, which showed Bridges had spent $113,000 in a three-month period on travel expenses and Crown limo costs.
Announcing the inquiry, Mallard said he believed someone had deliberately undermined the system, and the security of MPs was important.
"Unless they have incredible expertise they will be identified," he said.
Mallard believed the inquiry was a good use of taxpayers' money.
"Members of Parliament will not be able to do their jobs properly."
Where to get help
Mental Health Foundation
Free call or text 1737 any time for support from a trained counsellor.