Clayton Cosgrove signals the end of his parliamentary career after 16 years.

Labour MP Clayton Cosgrove is to stand down at - or before - the next election.

The list MP - who had held the Waimakariri seat for four terms - said it was not a decision he made lightly. He had discussed it with his leader Andrew Little,"who understands this is about new challenges and opportunities for me".

Cosgrove, 46, said he was elected when he was 30 and now was the right time to take the next step in his career.

Marion van Dijk "I will cross that bridge when I come to it." Maryan Street is next on Labour's list to enter Parliament if Clayton Cosgrove quits.

"Before entering politics I held senior executive positions in business both in New Zealand and Australia, and so I feel extremely fortunate to have gained so much experience in both the private and public sector," he said.

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​He was grateful to Little for promoting him into his shadow cabinet and to the two prime ministers he had worked for, "my close friend and mentor Mike Moore and Helen Clark".

Cosgrove in the Clark government was at different times minister for building and construction, immigration, small business, the Rugby World Cup, and associate minister for finance and justice.

"I consider my biggest achievements as a minister included the reforming of the real estate and property sector, lifting quality in the construction sector through the licensing of building practitioners and leading the development of the business case for the redevelopment of the Rugby World Cup flagship venue – Eden Park which led to Cabinet approval of $190 million for the project."

He was elected in Waimakariri in 1999 and held it until he was beaten by National's Kate Wilkinson in 2011. He lost to National's Matt Doocey in 2014.

Rumours Cosgrove planned to step down and seek a corporate job began circulating last year, but they faded after Little promoted him.

Cosgrove, who joined Labour when he was just 14 years old, said with seat selections looming he wanted to give Little flexibility and to give a replacement candidate in Waimakariri a fair go.

But there was no indication he would not have been re-selected if he had wanted to run again.

"It would be a devious journalist . . . who would try and make mischief out of this."

He still had "20-25 years of raw energy left in the tank".

"If you were going to make a move, now was the time."

He had told Little if another opportunity arose before 2017 he would have to consider it, so he could leave before then.

As one of the party's Right-leaning and business-focused MPs it is understood he was uncomfortable with some recent moves, especially Labour's opposition to the Trans-Pacific Partnership (TPPA) trade deal.

Cosgrove said he had "cut his teeth" with Moore when he was trade minister, and everyone knew where he stood.

"Equally ... I'm a professional. If the team has made a call that is the call and that is the position."

But in saying that he meant no disrespect to Phil Goff who was granted a dispensation to support the TPPA in light of his role in its early stages.

Cosgrove said Labour could win in 2017. Little was "a close mate of mine" who had unified the party.

"When people, as they are now, get to know the Andrew Little I know they will come to support him."

Little said he was working on the basis Cosgrove would likely remain an MP for the next 18 months.

The outgoing MP had offered to help including, as Cosgrove had described it to Little, "doing things that previously he couldn't do".

Little said he had not discussed the matter with former party president and MP Maryan Street, who would be the next list MP in line if Cosgrove quit before the election.

Street on her Facebook page she had called Cosgrove to wish him well.

But as far as taking up a list place was concerned there was "no decision I have to make at this moment."

"I will cross that bridge when i come to it."

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