Gerry Brownlee is defending his jaunt to Japan with Speaker Trevor Mallard to watch the All Blacks test.

The long-time National MP says they were on the ground for about 36 hours, busy with a programme facilitated by MFAT.

Brownlee says New Zealand has probably spent many tens of millions of dollars attaining the CPTPP, which will provide enormous opportunities to trade with all 11 countries - but more specifically Japan.

"We'll see the reduction of beef tariffs and other such. We want to have good contacts with the Japanese Government and their diet."

Brownlee's National colleague, long-serving MP and former Speaker David Carter did not seem impressed with the sojourn.

"The public will make their own judgement of it, but I would not have done it."

However, Brownlee seemed unfazed.

"Well that's okay. Previously there was no CPTPPA, for example, due to start on the first of December."

National leader Simon Bridges says it was a worthwhile trip, even though he wasn't consulted by Brownlee beforehand.

"I can understand people asking about costs and the like, but here we've got a situation of two senior MPs promoting Japanese relationships, I think that's a positive thing."

The Prime Minister also sees nothing wrong.

Jacinda Ardern says when it comes to trade, politics should be put to one side.

"Trade is something that has been treated in that ay for some time. We do go out and promote on behalf of New Zealand the trade interests of New Zealand."

The trip is said to have cost $24,000.