A sugar tax would generate millions in revenue and save lives, the Prime Minister has been told.

The briefing from the Ministry of Health's chief science advisor Dr John Potter was given at Jacinda Ardern's request.

Chief economist at the NZ Initiative Dr Eric Crampton told Mike Hosking there a few important details missing in the report.

"It's hard to tell to tell how much of this is new work and how much of it was from prior studies."

LISTEN ABOVE AS DR ERIC CRAMPTON SPEAKS TO MIKE HOSKING