Sir John Key has come out with a warning to rogue National Party MPs: "If you can't quit leaking, quit the party."
Speaking at National's AGM in Wellington on Saturday after it received a battering in the recent election, the former National leader and Prime Minister said MPs need to stop "going behind people's backs" with criticism.
"Here is my very simple advice to those who like to leak to the media - if you can't quit your leaking, here's a clue - quit the party," he said.
"The public look at it and say 'for goodness sake, if they can't run their own party, how on earth will they run a country'."
Sir John also warned National not to underestimate current Prime Minister Jacinda Ardern.
"Some people are going to tell you that eventually the public is going to get sick of Jacinda Ardern," he said.
"It is exactly what the Labour Party said about me for nearly a decade.
"If we underestimate Jacinda and her advisers, we will be in Opposition for a very long time.
"The public needs to hear our message, they need to hear us talking about them and their families.
"They don't want to hear us talking about ourselves. They have to be assured of our competence."
But Sir John also thought that Ardern was beatable.
"I think she's an empathy politician that communicates well. She's always had those - they're not new. That's her strength," he said.
"That doesn't mean she's not beatable. Bluntly, Nikki Kaye beat her a couple of times when I was the leader in Auckland Central.
"Anything's possible and things happen over time."
Giving her analysis of the election loss, National leader Judith Collins told the AGM National had been "far too focused on itself".
"We did not spent enough time talking about the things that matter to New Zealanders. The consequence of that can be seen in our election result and our reduced caucus," she said.
"We must give New Zealanders a reason to vote for us. We must be bold and inclusive. We have to motivate people to change the Government in 2023.
"People will not vote for change without reason. We need to convince them to have high hopes for themselves, to believe a better New Zealand is possible, to expect more from their Government."
National Party president Peter Goodfellow had a different message however, accusing the Labour Government of tyranny and calling it a "celebrity Government".
He said "reasoned debate became treasonous" during the campaign and characterised the daily COVID-19 updates as being "televangelistic".