John Key's new look: Champagne socialist?

John Key's snap with a bottle of Moet champagne has been doing the rounds on social media. Photo / Supplied

Prime Minister John Key was bubbling over with generosity on Saturday night as son Max celebrated his 18th birthday with friends.

A photo of Mr Key with a bottle of Moet champagne has been doing the rounds on Facebook and Twitter in the past few days.

The picture was taken during celebratory drinks at the family's Parnell home to mark Max's landmark birthday, which also means he's now old enough to vote for his dad.

Mr Key was asked about the picture just before he gave his leader's speech at the National Party northern convention on Sunday morning.

"Last night went well. Very well," the Prime Minister said.

"Did you finish it?" asked the Northern Young Nats chairwoman, Brittany Raleigh, of the bottle of Moet.

"Fortunately not ... They may have," Mr Key said, referring to Max and his friends.

Social Media NZ posted the picture on Twitter, prompting one tweeter to ask: "Is this supposed to be the new food in schools programme?"

"Expensive taste kids nowadays have if that's the case," another tweeter responded.

One wag suggested Mr Key was "channelling [Kiwi comedian] Dai Henwood" in the photo.