After being sent home by his leader for failing to front up on the credit card spending scandal, Labour MP Chris Carter has this afternoon offered a public apology.

"It is quite clear to me that a public apology is both demanded and required in regard to my expenses when travelling overseas on government business on the taxpayer expense," said Mr Carter.

"I unreservedly apologise to the New Zealand public.

"This has been a very difficult time for me and it has been difficult to choose the right words to be said when under intense pressure from journalists."

"I acknowledge that my temperament when under pressure can make me appear as if I am not contrite or embarrassed. I assure the New Zealand public, I am.

"I pledge hard work and commitment to my electorate and to the New Zealand Labour Party, and I wish to put this matter behind me."

Following Mr Carter's statement, Labour leader Phil Goff told reporters he accepted the apology but Mr Carter was "on notice".

"This is the minimum step that I demanded," said Mr Goff. "He now has to prove himself to me. For the time being he is on leave but when he comes back I expect him to behave in an appropriate way.

"He is on leave on my insistence for however long it takes. I expect when he comes back he would have thought through the consequences of his actions and I would expect to see a difference."

The conservation portfolio will go to David Parker in the meantime, said Mr Goff.

The Labour leader earlier today sent Mr Carter home and told him to consider his future because of his inadequate response to questions over his credit card spending and large travel bills on the taxpayer.

"I'm not happy with his response. I've sent him home and I've asked him to think about his future," Mr Goff told reporters today.

"His position as conservation spokesperson and within the shadow cabinet is in doubt at this point. I want him to calm down and to think about the consequences of his actions and to make a measured decision.

"I'm not happy with his acknowledgement about how the public feel about excessive expenditure on travel. I think he's under stress, he's under pressure, I understand that.

"I expect him to acknowledge why the public was concerned about excessive travel by ministers and MPs. He needs to do that."

Mr Carter was demoted yesterday from the front bench and stripped of the foreign affairs portfolio after the release of historic ministerial credit card details showed he had misspent money. In the reshuffle he was given the conservation portfolio, but dropped to number 13, just off the front bench.

Mr Carter repaid $251 last week, but has not acknowledged any wrong-doing or issued any apology.

He did not front to media yesterday, and today gave a short statement after the caucus meeting.

"Do I regret going off the front bench of the Labour Party and dropping the foreign affairs portfolio? I sure do. It's a great honour and privilege to be on the front bench and I've always been really interested in foreign affairs and it was always the job I most wanted.

"I'm really grateful that Mr Goff has given me the conservation portfolio. I loved the five years I spent as Conservation minister and I am looking forward to protecting New Zealand's unique landscapes and biodiversity."

Mr Carter did not take questions. He returned to the caucus room and, minutes later, left the building pursued by media.

He was then sent home by Mr Goff.

In an interview at the weekend, Mr Carter suggested he may quit politics.

"I just have to make a decision: Do I want to keep putting up with this? Do you want to live your life with this stuff going on all the time? You know, I love being an MP. But there might well be a point soon where I think this is just not worth it."