Christopher Luxon retains confidence in MP Joseph Mooney who said all Kiwis are guaranteed tino rangatiratanga under Treaty of Waitangi

The National Party leader continues to have confidence in one of his MPs who claimed "every single person in New Zealand" is guaranteed tino rangatiratanga (sovereignty) under the Treaty of Waitangi.

One academic described the comments by Southland MP Joseph Mooney, who's also the National Party's Treaty Negotiations spokesperson, as "an utterly incomprehensible interpretation of Te Tiriti".

Mooney at the weekend, posting on Twitter, commented on a news article about Local Government Minister Kieran McAnulty justifying keeping co-governance in its reset version of Three Waters. 

"I would suggest @Kieran_McAnulty has a read of Ko te tuarua (Article 2) of Te Tiriti o Waitangi and the guarantee of tino rangatiratanga to 'ki nga tangata katoa o Nu Tirani' - every single person in New Zealand," Mooney said.

His comments were blasted by Luke Fitzmaurice-Brown, a faculty of law lecturer from Victoria University.

"Joseph this is an utterly incomprehensible interpretation of Te Tiriti. Whatever you take the extent and limits of the Art 2 guarantee of tino rangatiratanga to be, there's no doubt at all (and never has been) about who it applies to," Dr Fitzmaurice-Brown wrote. "It's a guarantee to Māori - pure and simple."

National leader Christopher Luxon on Wednesday said he continued to have confidence in Mooney.

"We have big debates about the Treaty in this country… not ideal to be having it on Twitter and, also, I think Joseph got it wrong on this occasion but I've got confidence in him," Luxon told AM.

He wouldn't say whether Mooney could be his Treaty Negotiations Minister should National be elected in October.

"We'll talk about the Cabinet post-election," he told AM host Ryan Bridge.

Luxon also praised Mooney as a "hard-working guy".

"He just shouldn't have had a constitutional debate on Twitter."

Former Labour MP Darien Fenton said on Twitter Mooney's comments were "embarrassing", while historian Dame Claudia Orange told Stuff such rhetoric was how ex-National leader Don Brash "tended to argue, and it's really got no substance to it".