One political commentator has slammed Jacinda Ardern, before she's even confirmed as Labour's new leader.

Matthew Hooton told Chris Lynch the future of a 100-year-old institution is now in her hands.

"I think she'll fail. I think she's an absolute flake but obviously Labour Party caucus knows her better than I do and feels she's the right person to fill the shoes of Savage and Fraser and Lange and Clark."

Hooton said Ardern may succeed in salvaging some popularity among voters, but he can't see her forming a government on September 23.

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He said even if she did manage to bring together a three-party government made up of Labour, the Greens and New Zealand First he can't imagine for even a second Winston Peters playing second fiddle to Ardern, as her deputy prime minister.

Hooton said Peters would believe seniority counts for something and would absolutely insist on being prime minister.