Police have found no offence was committed when Winston Peters' NZ First party failed to declare an $80,000 donation as required by law.
The decision ends the open official inquiries into the NZ First donations controversy.
The police investigation related to a donation funnelled to the party from the Spencer Trust last year.
All donations over $10,000 are required to be declared, but NZ First subsequently filed a return to the Electoral Commission showing "nil" donations over $10,000 in 2007.
The police investigation began in September after Act leader Rodney Hide complained the NZ First return was false and that the party secretary had therefore committed an offence under the Electoral Act.
The police statement yesterday did not explain why no offence had been committed.
"Having assessed a range of information from various sources, and having considered the elements of the offence contained in the [Electoral Act], police are satisfied no offence was committed," it said.
A successful prosecution could have resulted in a fine of up to $20,000 and/or a year in prison.
The return was filed late on May 16 and the offence had a six-month time limit for charges to be laid, which runs out on November 16.
Mr Peters learned about the police decision while waiting to watch the Melbourne Cup in a corporate box at Ellerslie racecourse.
"I suppose the police would be able to wait till after the Melbourne Cup to do that, but never mind," he said.
Asked if it was too late, with NZ First struggling in the polls, Mr Peters replied: "Of course it's not too late. We'll get up on Saturday night."
Mr Peters said he had now been cleared by three independent investigations.
"There were thousands of hours wasted on the SFO, the Electoral Commission and the police," he said. "And all those allegations were baseless. Mr Hide should probably resign from Parliament and stop wasting everyone's time any more."
The Green Party this week called for another inquiry into the latest allegations in the Dominion Post newspaper linking NZ First and United Future to the wealthy Vela family, which co-leader Russel Norman said were the most serious yet "because they are allegations of money for policy".
The allegations date back to 1999 and stem from documents cited in the Dominion Post which indicate that former National MP Ross Meurant brokered donations from the Velas while working as an adviser to Mr Peters.
* Donations inquiries
Police: Complaint by Act leader Rodney Hide over failure to declare $80,000 donation in 2007. No offence found.
Electoral Commission: Found that while NZ First did not declare donation in 2007 it was not asking for a prosecution. Requested amended returns for 2005 and 2006 when there were also undeclared donations, although they were outside the time limit for prosecution.
Serious Fraud Office: Complaint by Mr Hide. Found no evidence of fraud but referred matters to the police, the Auditor-General and the Electoral Commission.
Parliament's privileges committee: Complaint by Mr Hide. Found Mr Peters knowingly provided false or misleading information by not declaring a $100,000 donation from billionaire Owen Glenn on the MPs' pecuniary register. Upheld by Parliament.