A senior New Zealand First MP has hit out at Winston Peters on the eve of the election - questioning his leader's behaviour and also criticising the party's marketing material.

New Zealand First MP Richard Prosser was demoted from third on the party list at the last election to 15th ahead of tomorrow's vote. On current polling that means he is unlikely to return to Parliament.

He has since taken to Twitter to criticise some of the party's marketing material, posting a photo of a pamphlet and asking "why in God's name is this brown??", and retweeting a reply from someone who wrote they were disappointed in New Zealand First for putting Prosser low on the party list.

And today an email from Prosser's Parliamentary email address was sent to the Newsroom website, questioning the "recent behavioural trends" of Peters.

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Prosser was responding to an assertion that he got NZ First policy wrong when he told a Business NZ conference that his party would bring back electricity assets to a simple state-owned, state-controlled umbrella.

A representative from Mercury Energy asked Prosser how he proposed to fund such a buy-back of electricity companies, given it would cost at least $11 billion.

Prosser said that would be done over time, but NZ First's stance was the institutions would be purchased back at the price they were sold for.

That caused Act leader David Seymour to use his speech to the same conference to call Prosser a "f***ing idiot", and Peters subsequently put out a statement saying Prosser's comment was a "throwaway line that was not fully explained".

"Had he had the time, he would have explained that the buyback of power companies would be at an appropriate time in the future," Peters said. "That is, we would only be buying back shares when they became available."

In the email to Newsroom sent from Prosser's Parliamentary email address, he says his statement concerning the re-nationalisation of power company shares was not wrong.

"Perhaps the Member for Northland had simply changed his mind and not bothered to tell anyone else. Or perhaps he had forgotten our established and agreed position. Or perhaps he simply forgot that he'd changed his mind," Prosser wrote.

"Recent behavioural trends lead me to suspect that any of the above are possibilities."

Prosser has been approached for comment. Peters, who is campaigning in Northland, wasn't aware of the email when contacted by the Herald, and said he had more important things to concern himself with, given today is the final day of campaigning.

Prosser has a reputation for causing the occasional controversy, with the first coming shortly after he entered Parliament in November 2011 over a column he wrote in Investigate called for the banning of the burqa in New Zealand.

Prosser's column, Eyes Right, ran in Investigate magazine for 10 years and was collected and published as a book, Uncommon Dissent: The Evolution of a Kiwi Nationalist, which included a description of Helen Clark's Labour Government as the "hijacking of New Zealand" by "a conspiracy of Silly Little Girls".

His column caused the biggest controversy of the MP's career in 2013 after he wrote that young Muslim men - or those who look Muslim - should be barred from flying on Western airlines.

That was reasonable, Prosser wrote, because New Zealanders' rights were being "denigrated by a sorry pack of misogynist troglodytes from Wogistan". The spur for the column was the confiscation of Prosser's pocket knife at Christchurch Airport.

Peters said he was disappointed in the comments and Prosser apologised and had dinner with a Muslim couple who wrote to the Herald to challenge his comments, arriving with a peace offering of a bouquet of flowers and a box of chocolates.