Mr Pearson, a veteran animal rights activist, concedes that he ate fish at the Sydney restaurant but described claims on a vegan community Facebook site he is a regular consumer of seafood there as "absolute rubbish".

"There was some fish on one of the dishes and I had a bit of it," he told Fairfax Media.

"I strayed for that moment; for that morsel. It's all over. I think the people in the party have forgiven me and now we have to get on and do the work for animals."

The AJP policy on marine animals states: "Eating fish, whether farmed or wild, is incompatible with AJP's advocacy of a plant-based diet."

Mr Pearson, who was elected to the NSW Legislative Council in 2015, regularly posts links to news articles about vegan issues.

In an interview for the March/April issue of The Australian Vegan Magazine he described himself as "almost vegan". In February Mr Pearson promoted an article on his Facebook page about the cruelty of eating farmed salmon.

Last week, as part of a story about his being interviewed by police over use of a drone to film a piggery, he told Fairfax Media: "I'm vegetarian".

"I'll be looking forward to the day when we don't rely so much on killing animals for food, obviously, but my main issue is how these animals are being killed," he said.

However, in March Mr Pearson was spied eating fish at a Japanese restaurant in central Sydney - a sighting quickly reported with great outrage on the Sydney Vegan Club Facebook forum.

"So the lead spokesman for the Animal Justice Party in the Government comes into my work regularly," a forum member wrote on the closed Facebook group in a post that was obtained by Fairfax Media.

"I work in a Japanese restaurant. Last night they ordered oysters and snapper fish. And they promote a plant based diet on their page, are so passionate about animal rights and the abolishment of everything cruel to do with it in Australia.

"Does anyone else find this a bit f---ed?"

Quizzed on the identity of the diner by fellow forum members, the poster confirmed it was Mr Pearson who, while dining alone, had ordered "oysters and snapper. Last few times he's ordered sashimi. I asked him about how to join the AJP as well".

Later, the member added: "I follow his page and support his posts and the AJP completely. It was really upsetting to find out how much of a traitor he is to these poor fish."

The post elicited a furious response, ranging from condemnation - "Such a f---ing hypocrite" - to defence, with one post reading: "When I think about all the good Mark Pearson has done for animals ??? I think he deserves some respect."

But Mr Pearson argued that "the main constituents of the party are not vegans or vegetarians".

"We did not get elected by the vegan community," he said.