The last piece of the puzzle is an ongoing federal prosecution of a company linked to Senator Hanson's chief of staff James Ashby over an alleged failure to comply with the Australian Electoral Commission's request for information.

Apart from the prosecution, AEC commissioner Tom Rogers said the One Nation investigation was "substantially finished".

Asked by Labor senator Murray Watt why the AEC did not take tougher action over the scandal, Mr Rogers said: "We've got a long-standing practice of accepting amended returns at any point."

"From time to time we get amended returns that go back a considerable period, but the key thing for us is disclosure," he said.

"From my perspective that is a reasonable result."

A Jabiru aircraft was bought and registered to Mr Ashby in June 2015, two months after Victorian property developer Bill McNee discussed the idea with the him and the One Nation leader, Senator Hanson.

Last year, Senator Hanson confirmed Mr McNee had "got the plane for James Ashby" and it did not go through the party office as a donation.

However, a series of public disclosures have now been made.

In March the AEC register was updated for 2015/16 to declare, under the heading "James Ashby", 243 flight hours in the Jabiru at a price of $125 an hour, not including fuel costs.

Mr McNee's Vicland group also lodged an amended donor return for 2014/15 in relation to two donations made to Pauline Hanson's One Nation totalling $57,720, relating to rent for a party office.

A further Vicland update for 2015/16 disclosed an amount of $98,175, which AEC chief legal officer Paul Pirani described as "approximately the cost of the Jabiru aircraft".

Mr Ashby still faces a possible fine of $1000 if the prosecution is successful.

He is also understood to be under investigation by the Civil Aviation Safety Authority for allegedly flying the plane without the correct pilot's licence.

Australian Associated Press