Labour leader Andrew Little has rubbished former Porirua Mayor Nick Leggett's chances of winning a seat next year as a National Party candidate.
Mr Leggett used to be a Labour member, but quit earlier this year so he could run for the Wellington mayoralty against Labour's own Justin Lester.
Mr Leggett had previously been tipped as a future leader of the party, but there are now rumours he might jump ship and stand for National in the Mana electorate next year, currently held by Labour's Kris Faafoi.
"I'm not particularly worried - we've got a fantastic MP in Mana who's established himself," Mr Little told Newshub.
"I said at the time when Nick stood for the Wellington mayoralty that he wasn't true Labour. He claimed that he was. He wasn't elected.
"I think that New Zealanders actually see through people who say they are one thing but they're not, and they get backed by the 1 percent to challenge Labour MPs and Labour candidates. I think people are past that so no, I'm not particularly worried."
Mr Leggett hasn't formally announced he will stand, but isn't ruling it out.
"I would never say never, but I say that in the widest possible sense," he said. "I won't rule out standing for any [party], I think that would be silly to."
Prime Minister John Key says if Mr Leggett decided to stand, National would take him "if he wanted to stand".
"I know Nick a little bit. I've had absolutely no discussions with him, but if he wanted to run for National, we take all-comers."
Mr Little also attacked Mr Leggett over his disloyalty to the Labour Party.
"People who are aligned to the Labour cause actually genuinely take action about improving housing, about lifting incomes, about making sure that schools are properly funded, and our hospitals are properly funded.
"What they don't do is go around looking for those on the highest incomes to back them - to challenge whoever because that's all they want. Labour people, passionate Labour in their heart - they stick with Labour, they campaign on Labour issues, and for the Labour Party. Nick's not one of those people."
Mr Little says there won't be any last-minute conversations to try to keep Mr Leggett on.
"I think he's pretty much said that he's not interested in Labour. John Key's calling him, and they're welcome to that relationship.
"I'm focused on the stuff that's about fixing New Zealand, and building a better New Zealand and I've got some fantastic Labour MPs, and some fantastic Labour candidates, and some emerging potential future talent that's going to do that.
"We've got a fantastic candidate in Mana, and in fact around Wellington and across New Zealand and we'll be putting up that fight next year. It is about presenting New Zealand with that choice."
National's previous candidate in Mana, list MP Hekia Parata, won't be standing for re-election.