Prime Minister Jacinda Ardern says Cabinet has made some decisions about the cannabis referendum in 2020 today, and Justice Minister Andrew Little will unveil them today.

She said the referendum was about putting a question to the New Zealand public, not about formulating a Government position.

She has said the referendum will be binding, but added today that making the referendum "truly" binding was challenging - and that Little would add more when an announcement is made this week.

"Announcements will be made very shortly."

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Ardern told yesterday's post-Cabinet press conference that said she had "very clear expectations" around Cabinet confidentiality and felt that those were upheld; Cabinet papers were sometimes circulated beyond ministers.

She had told ministers today: "All offices must equally maintain that confidentiality."

She said she would not hold an inquiry into the leaked paper that the National Party has partly released.

But she added she did not think this paper was leaked by a Cabinet minister.

She said there had been speculation about Cabinet paper leaks before, which she said was a serious issue. But she did not want to put resources towards an inquiry that may not yield any answers.