Former NSW deputy premier Troy Grant was advised in May last year to make public "as soon as possible" a landmark gambling harm report that recommends banning a controversial poker machine feature that was the subject of a Federal Court battle involving billionaire James Packer's casino company Crown.

But the NSW government sat on the report until October this year – almost two years after it was delivered – despite inquiries from its lead author, University of Sydney gambling researcher Professor Alex Blaszczynski, who "expressed frustration" at the delay.

The revelations are contained in emails and briefing notes released to Fairfax Media under government information access laws.

In October Gaming Minister Paul Toole finally released the report by the University of Sydney gambling treatment clinic, commissioned in 2013 at a cost of $263,000 and handed to the government in December 2015.