James Shaw fronts with the welfare numbers Marama Davidson forgot

James Shaw has defended his Green Party co-leader Marama Davidson, saying not every interview she gave on Monday was a "shocker".

Ms Davidson appeared on The AM Show to discuss her party's welfare policy, which includes boosting benefits by 20 percent.

Asked how much that would cost, she said it was a "fair question" but couldn't give any details.

"I don't have the full cost, but reasonable compared to what we lose when we don't allow people to make their ends meet," she told host Duncan Garner. "Too many people are struggling to make ends meet at the moment, and that's not good enough."

Garner excoriated Ms Davidson, saying she was "completely incompetent" and didn't belong in Parliament.

Mr Shaw told Newshub Nation on Saturday Ms Davidson has the full support of the party.

"Everybody has a bad interview sometimes. I've had some shockers in my time as well," he told host Emma Jolliff.

"I thought the response was a little over the top. Marama went on and had a couple of other interviews during the day which were a lot stronger than that. I think all of us in this business have had those kinds of moments."

Unlike Ms Davidson, he did have some figures at hand.

"In total, the package that we're talking about has an estimated cost of about $1.5 billion. But we have to work through some of the detail with the Government on some of that, because some of those costs are estimated.

"There are also savings on the other side of the equation, which when we did the original costings we weren't able to fully get. For example… enforcing sanctions, we spend over $40 million enforcing sanctions but we only retrieve about $30 million worth in return. We're actually spending more money enforcing a sanctions regime than we are from returning it. That was just what we were able to get at the time we were in Opposition.

"So we do have some estimates, but… part of the Budget process we have to go through is to make sure we can nail those down."

James Shaw, Marama Davidson and Julie Anne Genter.
James Shaw, Marama Davidson and Julie Anne Genter. Photo credit: Getty

Mr Shaw said the party membership are pleased with the wins the Greens are getting, despite only being a support partner to the formal coalition, and having to swallow dead rats like the waka-jumping legislation and having to approve controversial water bottling contracts to overseas companies.

"We had an AGM about a month ago and I was actually pleasantly surprised at just how pragmatic people are being about the fact that being a part of a Government - and a minor party in a Government - means that you don't get everything that you want all of the time.

"But the things that we are winning - like the Zero Carbon Bill, like the largest increase in Department of Conservation funding in 16 years, like the transition to a more fuel-efficient, less-emitting fleet, all of those things, they're actually worth it. We know there are battles along the way we're not going to win, and I think people are generally pretty reconciled to that."