National leader Simon Bridges has lashed out at former MP Jami-Lee Ross, calling him a "terrible person" and accusing him of defamation.
But Bridges said he was not likely to launch legal action against Ross, as it was "hardly worth the time and the effort".
Ross made good on his promise today to go to the police with accusations of electoral fraud against Bridges.
After speaking to media, after a two-hour meeting with three investigators, Ross released a six-minute tape of a conversation he secretly recorded with Bridges.
The tape revealed Bridges calling list MP Maureen Pugh "f***ing useless".
Bridges fronted media after the tape was released and offered a "heartfelt apology" to Pugh.
"I have apologised profusely to her for my wrong comments," he said.
"I am mortified. There is no excuse for them."
He said the recording was a "blunt, private conversation" and "I obviously didn't mind my Ps & Qs".
"I am something of a rough diamond sometimes. I'm not perfect."
He said this had been a "big and hard lesson" for him to have learned.
Bridges called the recording a "monumental breach of trust" which showed his leak investigation was the right move.
"Jami-Lee Ross is a person who lies and leaks and, in this conversation, he deliberately tried to set me up," Bridges said.
At the heart of Ross' corruption allegations is a $100,000 donation to the National Party.
Ross claims Bridges asked to have that split into smaller payments.
The tape did not reveal Bridges asking this to happen, but it did reveal the National leader acknowledging a $100,000 donation had been made.
Bridges said the tape showed he had done "absolutely nothing wrong".
He said Ross' police complaint was "bogus, stupid and vexatious" and he was not worried about the police investigation.
Bridges told media on May 14 he attended a dinner with Yikun Zhang because Ross knew him well and was incredibly keen that they meet.
On May 21, Bridges said he attended a dinner for fellow National MP Paul Goldsmith at which Zhang was present.
"He told me that he and his supporters wanted to donate a large sum of money, around $100,000, and I thanked him and made clear that's something Jami-Lee Ross should deal with."
Bridges said he could not recall other subsequent calls, but is adamant the tape did not back Ross' "lies to the [media] over that last 24 hours".
"He has defamed me, and he is a liar."
He believed Ross had been secretly recording him for many months and may have been recording other MPs: "It's a monumental breach of trust".
Bridges said the $100,000 was seven donations from eight people.
Asked why he didn't explain that yesterday, he said it's "because I'm a lawyer".
"I'm a cautious person who takes things seriously and I take this seriously. It was a very serious allegation of corruption."
He said when speaking to media yesterday, he wanted to make sure he had done his due diligence and talked to that National Party about things that were "news to me".
In the tape, Bridges said having two Chinese MPs would be "nice", but putting them on the list and keeping everyone happy would be "bloody hard".
"Depends where we're polling ... that sort of thing. Two Chinese would be nice but would it be one Chinese and one Filipino. What do we do?"
Asked if he owed the Chinese community in New Zealand an apology, Bridges said no.
"I don't think there is an apology needed there – it was a frank conversation. I think New Zealanders would understand what I was trying to say."
Pugh later tweeted that she was disappointed to hear today's comments.
"But Simon has apologised and I have accepted that. I probably have annoyed Simon at times because I'm a fierce advocate for West Coast/Tasman...
I'm always in his ear, at times pushing the envelope for what is right for my community. I'm glad that JLR a man who deliberately released a recording that he knew would embarrass me is no longer in our caucus. I continue to back Simon and we'll both move on from this now."