A NSW Greens MP has told a budget estimates hearing he broke the law by eating cannabis on Friday morning, to prove a political point about hemp-based foods.

Jeremy Buckingham made the confession before asking Primary Industries Minister Niall Blair why it was illegal to consume hemp seed in New South Wales, stifling a potentially lucrative industry.

The ABC understands Mr Buckingham had eaten some certified organic hemp seeds before attending the hearing.

According to Food Standards Australia and New Zealand, hemp is a source of protein, vitamins, minerals and omega-3 fatty acids.

Low-THC hemp can be grown in NSW under licence, but it is used for its fibres and oil, not for food.

Mr Buckingham, the Greens agriculture spokesman, has campaigned for farmers to be allowed to sell hemp seed for human consumption, to make the crop more viable.

Mr Blair appeared momentarily taken aback by Mr Buckingham's admission:

Mr Buckingham: Minister you may or may not be surprised that this morning I consumed cannabis. I broke the law. Mr Blair: Camus? Mr Buckingham: Cannabis. Mr Blair: Oh cannabis. Mr Buckingham: Minister, why are standing in the way of a billion-dollar hemp food industry? Mr Blair: Do you want me to comment on the first part of the question?

In May, the MP lit up an e-cigarette in Parliament to prove a point about legal loopholes around the vapour devices.

He said e-cigarettes should be dealt with under the same laws covering tobacco and nicotine, including banning their use in non-smoking areas.