Things were coming to a head between then-National leader Simon Bridges and MP Jami-Lee Ross in September 2018 when Ross secretly recorded a heated conversation with his colleague in which Ross offered an ultimatum: abandon plans to demote him or prepare for an improper donation scandal.

"The problem we have is you've asked me to go and collect [a] $100,000 donation. That donation has not been declared properly," Ross said in the conversation, which was replayed in the High Court at Auckland today as Bridges sat in the witness box. "..Those donations have not been handled in a way that's in accordance with the Electoral Act.

"You've put me in a position where if I have to lose my career I have no option but to go down fighting. I don't think that's helpful to you. I don't think that's helpful to me.

"...I cannot go to the backbench - I'm not going to go there willingly. You would have to force me there, and then we would have a very public fight because I think that would be very damaging to you too. And you and I both have a lot to lose over this, because breaches of the Electoral Act around donations are very f***ing serious."

Ross is now one of seven defendants in the Serious Fraud Office trial, which involves allegedly illegal donations by Remuera-based Chinese businessman Yikun Zhang to National and Labour. Bridges, who is now retired from Parliament, was never charged with any wrongdoing.

Jami-Lee Ross in on trial in the High Court at Auckland, accused of helping to facilitate an illegal political donation. Photo / Jason Oxenham

The judge-alone trial before Justice Ian Gault, now in its third week, started last month with each defendant pleading not guilty.

After the long soliloquy in the secret recording in which Ross aired other grievances, Bridges thanked him but immediately zeroed in on Ross' donation reference.

"I think firstly on the donations issue, I'm absolutely certain I have never asked you to do anything illegal," he said. "I have absolutely no doubt of that because I know my morals and my integrity and I don't accept that within it.

"And I don't say that in any way other than saying to you that is not going to be a factor in my consideration."

Less than a month later, in October 2018, Ross told media about the donation, positioning himself as a whistleblower to what he said was corruption by Bridges. Ross went to police the next day, handing a detective recordings and documents that are now being used to prosecute him instead of Bridges.

That donation was the focus of Bridges' testimony today.

Bridges said he remembered having dinner at Zhang's home alongside Ross and his wife in May 2018. He might have met Zhang at one or two prior events, but he didn't know the businessman personally, he said, explaining that Ross would have organised the dinner.

Prosecutors showed the former politician a photo from the dinner in which he sat between Ross and Zhang, with co-defendant Colin Zheng - described as Zhang's right-hand man - also sitting next to them.

Four of the seven accused in the political donations trial are Yikun Zhang (left), Shijia (Colin) Zheng, Hengjia (Joe) Zheng and Jami-Lee Ross. Photo / Jason Oxenham

There was "no detailed discussion at any level about donations" during the dinner, Bridges said, but he acknowledged the gathering was "in that context" of a possible future donation.

Ross told police that he got a call from Bridges a week later in which the party leader said Zhang had committed to a $100,000 donation but didn't want it made public. Bridges acknowledged having called Ross that night after running into Zhang at another event and learning of the donation.

But he would never have concerned himself with collecting donations himself or instructing others how to go about processing them, Bridges said.

"It's a big, many-thousands person organisation ... but as leader I certainly didn't, wouldn't," he testified. "You simply don't get involved in things you don't have time for and are other people's responsibilities."

Ross told police he then naively "acted on my leader's instructions", collecting the $100,000 donation, which was then split into smaller donations that were below the $15,000 declaration threshold. He gave police a list of people whose names were then put on the lesser donations.

Donations totalling more than $15,000 over the course of a year must be disclosed to the Electoral Commission, according to the Electoral Act.

Ross told police he didn't record the initial phone conversation with Bridges, but he would later secretly record another call with Bridges followed by two conversations in Bridges' Parliament office that would later be played in court.

When asked again on the stand if he had ever given Ross instructions to collect the donation in a covert way, Bridges responded: "I reject that entirely".

His testimony continues.