New Zealand First leader and Foreign Minister Winston Peters is defending his party's switch to support the newly negotiated TPP, saying enough changes have been made to the deal to allay their concerns.

Photo: AFP

After a breakthrough at talks in Japan in recent days, 11 countries, including New Zealand, are preparing to sign the agreement in Chile on 8 March.

Mr Peters and his party have opposed trade deals in the past, including the FTA with China while he was foreign minister, negotiated under the Labour government led by Helen Clark.

He also campaigned against the TPP, describing it at Rātana in 2016 as a "sham and a scam".

But he told Morning Report the deal has been renegotiated, since the Labour-led government took office.

"The deal is not the deal inherited, it's different ... with substantial changes with the types that the Canadians were holding out on as well, that we both have seen changes that mean we can support this deal".

The sticking point for New Zealand First had been the rules under which foreign companies can sue governments, the investor state dispute rules.

Photo: RNZ / Richard Tindiller

Speaking from London, Trade Minister David Parker confirmed changes to those rules had been "limited in scope".

RNZ understands the changes mean foreign companies would not be able to take legal action - under the specific dispute provisions - relating to government contracts.

New Zealand already an exemption to the those rules with Australia, but Mr Parker said carve-outs with "various other countries" have been negotiated.

Mr Peters also said the government has now retained its sovereign right to ban foreign purchases of residential houses in the deal, now called the CPTPP (Comprehensive and Progressive Trans-Pacific Partnership).

"We were shocked to find out upon becoming the government, [it] had never even been raised by the previous government and so we were going in there to see why they were insisting on that, and we were shocked to find out the National Party had never raised it in the first place."

Mr Peters said he had not the seen the final text that was likely still being drafted, but he knew the details of the principle changes his party now intended to support.

Mr Parker said the substantive text was already public and the small appendix containing the changes negotiated since last November would be made public close to the signing date.

The National Party has demanding the Labour-led government release the details before the deal is signed.

The government will need National to pass the enabling legislation.