Foundation 51, the company labelled in NT Parliament as a "CLP (Country Liberals Party) slush fund", has submitted new documents showing it received hundreds of thousands of dollars in the year leading up to the 2012 election.

The submission comes just months after a special police unit began investigating the company.

The NT Labor Opposition has before accused it of being a "slush fund" through which the CLP could receive monies that otherwise, by law, would have to be declared.

Labor NT president Syd Stirling said the late submission of Foundation 51's annual return for a period ending nearly three years ago "beggars belief".

"Of course, 2012 was an election year," Mr Stirling said.

"But ... what are they trying to hide with this $263,000?"

Annual returns for years after 2011-12 had previously been submitted by Foundation 51, but never for a year before the election.

This is in spite of correspondence — revealed by the ABC last year — between Foundation 51 director Graeme Lewis and senior CLP executives detailing hundreds of thousands of dollars the foundation spent on election activities in the lead up to the 2012 poll.

Mr Lewis told the ABC he had "lost any will to fight the (Electoral Commission)" and so several weeks ago submitted an annual return for 2011-12 detailing receipts totalling $263,201.

"As I saw the rules at the time, no, I don't believe I made any mistakes."

"I still don't."

Foundation 51 Director Graeme Lewis

The annual return lists developers such as John "Foxy" Robinson, Sitzler, Gwelo, Halikos and Randazzo Properties, and businesses such as Coleman Printing, Airnorth and Sherwin Iron, who paid varying amounts up to $6500 to attend "seminars".

"The seminars had people like Andrew Liveris from Dow Chemicals — he gave a speech, he's a magic bloke," Mr Lewis said.

"Another one was (mining magnate Andrew) Twiggy Forrest, who came to talk about his Aboriginal employment initiatives."

Some of the larger payments — worth up to $55,000 — were listed under "consultancy" for companies including DIAH (Darwin International Airport Hotel) Pty Ltd, Bjaat Pty Ltd, and Northwest Constructions.

"(One company wanted) research into their business of providing workers' camps ... we were doing research on public opinion and how the public would react," Mr Lewis said.

NT Electoral Commission probe into processes

Foundation 51 is a private company with close ties to the governing CLP.

It was set up in 2009 by Mr Lewis, a long-time CLP identity, and then CLP opposition leader Terry Mills' chief of staff James Lantry.

Mr Lewis and the CLP had previously argued there was no connection between Foundation 51 and the party.

But the NT Electoral Commission (NTEC) began a formal investigation into the company in August last year after Labor lodged an official complaint, asking whether Foundation 51 fell under the definition of "associated entity".

Under the NT Electoral Act, an associated entity operates wholly or significantly for the benefit of a political party.

The month after the NTEC began investigating, Foundation 51 began submitting associated entity annual returns but only covered periods after the 2012 election.

In April, the NTEC handed over its investigation to a special police unit that has been set up to deal with corruption matters and cases of a sensitive political nature.

That has now been followed by Foundation 51's submission of an annual return for 2011-12.

Mr Lewis told the ABC he did not, until now, submit an annual return for that year because he believed the role of Foundation 51 was different before the 2012 election — focused on doing research for companies and holding business development events.

But he conceded pressure, a police investigation and what he called "grey" legal definitions led to the latest disclosure.

He said he still believed Foundation 51 never properly fitted the associated entity definition.

The NTEC refused to comment on the late submission of the annual return, as it had "referred its investigation into Foundation 51 to the Northern Territory Police".

The NT Police did not respond to questions about the status of the investigation.

Under the Act, failure to comply with rules to do with returns can be prosecuted within three years of the offence.