Green Party MP Mojo Mathers says she is a beneficiary of a UK-based family trust - not a foreign trust.

Greenpeace boss and former MP Russel Norman says John Key is using "discredited allegations" that Greenpeace gained from a foreign trust to score political points.

During Question Time on Tuesday the Prime Minister told Green Party co-leader James Shaw, who replaced Norman last year, that he should speak to Greenpeace about why they're implicated in the Panama Papers.

Key said there were "quite legitimate reasons why people have a foreign trust" and told Shaw to leave the House and "ring Greenpeace, Amnesty International and Red Cross because they are implicated in the papers".

In the House John Key accuses Greenpeace and Green MP Mojo Mathers of benefiting from foreign trusts after being questioned by Green Party leader James Shaw about Mossack Fonseca.

But Norman says the reference is to old papers from 2013, which have already been "discredited" after it was revealed rich investors had been naming charities as trust beneficiaries to avoid scrutiny by tax authorities.

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As part of an investigation by The Sunday Times and the International Consortium of Investigative Journalism in 2013 it was revealed Paul Hogan, the Crocodile Dundee actor, was investigated for illegally evading tax.

He had placed $34m in the offshore Carthage Trust, which listed the British Red Cross as the beneficiary.

Reports show Hogan later admitted this was a sham to "protect his privacy".

Norman said Greenpeace had never received money from foreign trusts and it was a "completely wild allegation".

"These people use the names of charities to put people off what they're doing."

Norman said Key was "mud-slinging" in an effort to "muddy the waters on the issue".

"He should deal with the issue at hand and crack down on tax avoidance".

On top of the Greenpeace allegations Key also took a swipe at Green Party MP Mojo Mathers, who along with National MP Paul Foster-Bell, has been linked to a foreign trust.

During Question Time Key told Shaw to "just turn around and ask his colleague, Mojo Mathers, (who) has a foreign trust".

Mathers sought leave in the House to dispute Key's claims and clarified she was a "beneficiary of a UK-based family trust".

"It is not a trust that I own, and it is not a foreign trust," she told the House.

Labour leader Andrew Little later defended Mathers and said Key's comments were "dumb" and "totally tasteless".

"If he was a man he would stand up and apologise, he didn't do that."

"She should never have been put in that position. She's the only deaf member in the House and this is New Zealand sign language week. It was just totally tasteless," he said.