ACT leader Rodney Hide has laid a complaint with police over New Zealand First's return of donations for 2007.
Mr Hide alleges that New Zealand First's nil-return is false, after the Spencer Trust confirmed it made a payment to the political party last year in excess of $10,000.
Radio New Zealand understands about $80,000 was paid into New Zealand First's main bank account by the trust in December last year.
All donations to political parties in excess of $10,000 must be declared, but New Zealand First has never declared any money from the Spencer Trust.
Speaking outside Police National Headquarters on Thursday, Mr Hide said he was sure police will want to clear up the matter.
Mr Hide said with the Spencer Trust now saying it made donations larger than $10,000 in 2005, 2006 and 2007, New Zealand First's failure to declare looks systematic, and it's time the party offered an honest explanation of what has been going on.
On Thursday, New Zealand First leader Winston Peters dismissed Mr Hide's complaint as "obsessive, compulsive grandstanding."
Mr Peters says the complaint is a complete waste of time, and New Zealand First intends to clarify some very simple issues giving rise to a misrepresentation in the public arena.
Complaint to Electoral Commission
The Electoral Commission has received a complaint about New Zealand First's return of donations for 2007 and says it is keeping a watching brief on the matter.
The trust has confirmed it made payments to New Zealand First of more than $10,000 in both 2006 and 2007. Radio New Zealand understands the 2007 payment was close to $100,000.
The Electoral Commission says it is watching developments closely, and if necessary it could refer the matter to police for investigation.
Any prosecution would have to commence before mid-November.
New Zealand First president George Groombridge has written to the commission about the party's donation returns.
The commission says the correspondence relates to the 2005, 2006 and 2007 returns, but says it is unable to disclose the contents of the letter. It says it will consider the letter and options for possible further action at its meeting on Monday.
Mr Groombridge says the party has nothing to hide, adding that he would be extremely surprised if the commission took any action against New Zealand First.
The trust has previously confirmed it transferred $50,000 to the political party in September 2005, including $25,000 from businessman Sir Robert Jones. The donation from Sir Robert was not declared in the party's electoral returns.
Sir Robert's donation, and others by the Vela family to New Zealand First, are the subject of an investigation by the Serious Fraud Office.
Mr Peters, the party's leader, has stood down from his ministerial duties including that of Foreign Affairs Minister while the inquiry is carried out.
A trustee for the Spencer Trust, Grant Currie, says all money intended for New Zealand First has been paid out to the party, including payments in 2006 and 2007.
Mr Currie says the amount of those payments is confidential, as is the name of donors to the Spencer Trust. He says the trust has not done anything for some time, and now has only about $900 on its books.
New Zealand First has never declared receiving donations from the trust, and says the failure to do so in 2005 was a result of human error.
Auditor blamed for donation error
The lawyer for Mr Peters, Peter Williams, QC, is blaming an auditor for New Zealand First's failure to declare Sir Robert's donation.
Mr Williams says it is now clear that all the money intended for New Zealand First did reach the party, and there has been no fraud.
He told Nine to Noon on Wednesday that his understanding is there was a mistake made by an auditor who did not pick up the fact that that particular sum had not been registered.
"That apparently is the only mistake they've made, their books are pretty impeccable over a period of 15 years."
Mr Williams says about $80,000 in donations from the Vela family were paid to the Spencer Trust and from there to New Zealand First.
He says New Zealand First is the target of a witch-hunt, and as far as he is concerned the SFO should bring its investigation to a close.
Error by NZ First staff, says auditor
In a letter released on Tuesday, New Zealand First's auditor Nick Kosoof said an administrative error prevented the donation, which was was part of $50,000 paid to New Zealand First's account in 2005, from being declared.
Mr Kosoof said he has been informed by New Zealand First that the error occurred during a period of staff changeover and voluntary officers who were new at the time may have been unaware they were required to declare the donation from Sir Robert.
However, he admits the issue could have been looked into sooner. Mr Kosoof says the remaining $25,000 was not required to be declared, as it was made up of individual donations of under $10,000.
It is now legally too late for New Zealand First to be prosecuted for not declaring the money in 2005.