The Serious Fraud Office (SFO) has signalled an announcement is imminent over its inquiry into National's handling of an alleged $100,000 donation.

Photo: RNZ / Rebekah Parsons-King

The agency launched an investigation in March 2019 into National Party donations after the police referred on a complaint by former National MP Jami-Lee Ross.

In response to queries from RNZ late last week, the SFO first said they had "no updates" on the case, but then confirmed it was planning an announcement.

"SFO investigations take some time because of the complexities involved," a spokesperson said.

"We intend to make a public announcement regarding this case in the upcoming weeks."

Ross - who is now an independent MP - dropped the bombshell allegations in October 2018, claiming National leader Simon Bridges had asked him to collect a $100,000 donation from a wealthy businessman.

He said Bridges had stressed it should not be made public. The money then arrived in chunks smaller than $15,000, the threshold at which donations have to be declared, Ross said.

Both National and leader Simon Bridges have denied any wrong-doing.

Law professor Andrew Geddis, from the University of Otago, told RNZ he hoped the SFO announcement would bring the public some clarity well in advance of election day.

"Ideally, it would be good to have the Serious Fraud Office report on what they found ... as soon in the year as possible," he said.

"It'd be good if we had an election that was focused on the issues, rather than on [speculation over] whether there has been or has not been some sort of wrongdoing."

Auckland University associate law professor Tim Kuhner said the investigation's findings would be significant as the complaint went to the heart of transparency and democratic integrity.

"New Zealanders need all the information they can get on where political parties are getting their money, and what the strings are, that are attached to that money."

Kuhner said he trusted in the SFO's "neutrality and professionalism" to properly conduct its inquiry, but agreed that the sooner it could reveal its findings, the better.

"Obviously, there's political implications either way. For National, it simply looks bad to have a pending investigation, whatever the eventual result is.

"But I think the greater issue is ensuring that voters have the information they need to make an informed decision."

A spokesperson for the National Party referred all questions to the SFO.