We've done what National said we couldn't with CPTPP - David Parker

Trade Minister David Parker says the Labour-led Government has achieved something the previous government said it never could - signing the Trans-Pacific Partnership (TPP) while banning foreign home buyers.

He told The AM Show on Thursday morning New Zealand had issued five demands in negotiations over the revised TPP before agreeing to sign it - including protecting the Treaty of Waitangi, the Government's right to regulate, and Pharmac.

But they also successfully negotiated a ban on foreigners buying New Zealand homes alongside getting the newly-named Comprehensive and Progressive TPP (CPTPP) over the table, he says.

"That one, we were told by the previous government couldn't be done," Mr Parker said.

"We were told we either had to have CPTPP or ban foreign buyers, that we couldn't do both. We've proven that we can, in fact, achieve that."

Mr Parker also rebuffed National leader Bill English's claim that free-trade negotiations with China could scuttle the ban.

The former Prime Minister told The AM Show on Tuesday that trying to get an upgrade on trade with the Asian nation while effectively banning its citizens from buying homes here would be "a big test".

"They've yet to see whether the Chinese are going to take a deal where they give us something for our dairy and agricultural produce - which is really important to us - but whether they'll take worse treatment than Australia on this housing issue," he said.

But Mr Parker explained that while the Ministry of Trade and Foreign Affairs is still attempting to nut out lingering issues with Singapore, the rest of the world seems to understand why the Government is eager to make the change.

"Everyone else is struggling with what to do to protect your own people from the consequence of this incredible concentration of wealth at the top, where you've got some super rich people," he said.

"It really is those super rich people that can come to New Zealand and compete to buy the most beautiful island in the Bay of Islands - or the most modest home in south Auckland, which is nonetheless someone's dream.

"It's interesting: those politicians overseas have got an eye on what we're doing - not because they're critical, but because they're struggling with some of these same issues at home."

Mr Parker says Deputy Prime Minister Winston Peters, who has been strongly against signing any version of the TPP in the past, has still not made his stance on it clear. He says discussions with him and NZ First over the matter are on-going.

The Greens won't be supporting it, he added. The party has said in the past that as long as foreign investors have the ability to sue our Government, it wouldn't offer its support.

The Greens - and New Zealand First - have long opposed the TPP, with the most-raised issue being the potential use of investor-state dispute settlements (ISDS) mechanisms. Those mechanisms are controversial, as they allow companies to sue a Government that violates the company's rights under the treaty.

Mr Parker says although they weren't able to get rid of that proviso, changes have now been made to ensure it's less likely.

"[A company] could allege they didn't like our laws, but there's very strong protections in there that mean we can do essentially anything we need to - in the environment space, with taxes, health and safety laws, labour laws, all those sorts of thing.

"Also the scope of ISDS clauses, although we didn't get rid of them completely, we narrowed them.

"Previously, if you were an overseas company building the Waterview Tunnel and you were dissatisfied and had a dispute, you could sue the New Zealand Government through an international disputes tribunal.

"Now, you can't - you just have to sue like everyone else through the New Zealand courts."

Mr Parker says New Zealand has also narrowed the effects of ISDS clauses by signing a number of bilateral deals with Australia and other countries.