Sir William Gallagher is sticking by comments he made during a speech to business leaders at Waikato Stadium on Friday night.

Waikato business leader Sir William Gallagher is under fire after claiming the Treaty of Waitangi is a farce.

While Sir William, who made his fortune in fencing, made the comments during a speech to businesspeople at Waikato Stadium on Friday, he was happy to expand on the topic on Sunday.

The Treaty papers on display at Te Papa were fraudulent documents and the concept of the Treaty itself was a rort, he said.

"It was addressed to all New Zealanders, not native New Zealanders," he said.

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"There is no doubt [Māori] gave up sovereignty ... and now we have these bloody reparations going on."

The Foreshore and Seabed Act was an example of the Government handing over the rights of all New Zealanders to Māori, he said.

"Don't think it's not happening. Just go to the south end of the beach at Whiritoa and try to go for a walk there. There is netting there - that's the Māoris trying to fence it off.

"It's separatism. This is apartheid. There is no definition of Māori ... You are Māori if you feel you are Māori."

Before the arrival of Europeans, cannibalism was rife, he said.

Sir William joined the company his father founded, Gallagher Group, fresh out of university in 1962 and has worked his way up from the shop floor to become chairman and chief executive. It is known internationally for fencing systems. Gallagher Group is also a major sponsor of the Chiefs Super Rugby team.

He was made a member of the British Empire in 1987, a companion of the New Zealand Order of Merit in 1999, and was knighted in 2010.

Even the words "Māori" and "Aotearoa" are misnomers, he said on Sunday.

"Māori in 1840 meant 'normal' or 'common'. It was not until 1850, 10 years after the Treaty was signed, that it was used to refer to native New Zealanders," he said.

Aotearoa was the creation of "a guy called Smith", he said, in apparent reference to Judge Thomas H Smith of the Native Land Court, who used the term in his 1878 translation of the national anthem God Defend New Zealand.

Sir William said he was well aware some might find his views inflammatory, however he stood by them and had numerous sources informing his stance.

He referred to the Hobson's Pledge campaign, as well as the 2015 book One Treaty One Nation by Hugh Barr, both of which had been championed by former National and Act party leader Don Brash, but also denounced as racist propaganda by others, including former UnitedFuture leader Peter Dunne.

The chairman and chief executive of the Gallagher Group had been invited to speak at a Christmas cocktail function hosted by the Waikato branch of the Institute of Directors.

During Sir William's speech, which also included references to climate change, about half a dozen audience members walked out.

An estimated 70 to 100 people attended the function.

One audience member who declined to be named said Sir William's speech was not well-received and had left some upset.

He described Sir William as articulate and passionate during his talk.

"His speech started off all very convivial, with Sir William reminiscing ... and then it went quite left field," the man said.

"He started saying the Treaty of Waitangi is a fraudulent document and the copies that exist aren't true to the original draft. He didn't seem anti the Treaty but he seemed to think it was a bit of a farce.

"A lot of people were squirming in their seats because the speech was so non PC. It certainly ruffled a lot of feathers."

The man said many in the audience held Māori governance roles.

Sir William told the group he had done a lot of research on the Treaty and could support his views with reputable sources. He invited audience members to talk to him afterwards about the topic.

"He was basically referring to a big Treaty cover-up."

Sir William also questioned scientific evidence supporting global warming, saying during the 1970s scientists had predicted a new ice age.

They were topics he was all to happy to expand on in person on Sunday.

He could not recall anyone walking out as he was speaking, but he does recall "a muted reaction" to his thoughts on the Treaty.

"I got the silent treatment a bit," he laughed. "It was meant to be lighthearted ... There was plenty of laughter earlier on, and then none at all."