A former New Zealand First president says the anonymous leaks of sensitive party documents must be coming from someone who holds or held a high position in the organisation.

Photo: RNZ /Dom Thomas

And a former MP estimates only about half-a-dozen people could be responsible.

A database containing the personal details of hundreds of NZ First members was sent to media outlets and opposition MPs this week, hot on the heels of another anonymous leak of internal complaints the week before.

NZ First leader Winston Peters - who's also Deputy Prime Minister - denounced the leak as a "deliberate and malicious misappropriation of data by a disgruntled source" and promised to refer it to the police and privacy commissioner.

Kevin Gardener - who was party president from 2010 to 2013 - told RNZ the leaks would have to have come from someone "well up" in the organisation.

Even board members did not have easy access to members' personal information or letters of complaint, he said.

"Even as a party president, I did not have access to membership details. I had to ask the membership secretary ... and the lady at the time guarded that with her life."

Mr Gardener was ejected from NZ First late last year and told it was due to him joining another political party - which he denies doing.

But he told RNZ he was not responsible for the leak and was not upset about how he was treated.

"That's the way New Zealand First deals with things."

Mr Gardener acknowledged the leaks spoke to an element of discontent within NZ First, but he doubted it was more pronounced than in any other party.

'Hardly the stuff of great scandal'

In another blast from the past, former NZ First MP Richard Prosser published a blog post online in which he too denied any responsibility for the leak.

He described the release of sensitive material as "a bit of an embarrassment" but "hardly the stuff of great scandal", and said the leaker and their motive was of more interest.

"For the record it wasn't me," Mr Prosser said in the post.

"In fact the number of people who would have access to that sort of information from within the Party itself isn't great... There are probably only half-a-dozen people who could have known."

Mr Prosser - who has recently moved to the United Kingdom - entered Parliament in 2011 and held a high party ranking for many years.

He criticised Mr Peters and the party's campaign just before the 2017 election after being shunted down to an unwinnable list placement at number 15.

NZ First heads into its annual convention in Christchurch on 18 October.