For the sake of NZ First's future as a party former MP Richard Prosser said they should go left.

Mr Prosser was bumped down the party's list ahead of the election and lost his place in parliament as a result.

He was back in the building on Wednesday morning to finalise his departure but despite still being a member of the party was banned from the floor where the party's caucus is meeting to reach their decision.

"I still think they'll go left if they possibly can," he said.

"The danger of going right and propping up a fourth term National government, the odds of them getting a fifth term are pretty slim and if you're associated too closely with that when they go down you go down with them as a small party."

But he said the Green Party was a possible sticking point because of the "gulf of differences" between the two parties.

Mr Prosser expects if leader Winston Peters gets what he wants in these negotiations this could be his final term in parliament, provided there's a strong succession plan.

"No-one lives forever in life or politics and one day Winston will go and when he does someone will replace him," he said.

There's some weight to the idea that Mr Peters would favour new MP Shane Jones as his successor but deputy Ron Mark has the majority support of membership while third ranked MP Tracey Martin is also a strong contender, he said.