Badger Trust CEO Dominic Dyer told ITV News that Princess Anne is wrong to recommend the gassing of badgers.
"Princess Anne is fundamentally wrong," he said.
"Badger gassing does not work. It is very ineffective because you're pumping gas into a set with lots of tunnel entry and exit points.
"The gas does not disperse equally - it won't kill all the animals outright. On average 20-30% of them will die prolonged, long deaths or suffer brain damage as a consequence.
"So it's not effective and it also has huge humaneness issues associated with it as well."
More top news
Prime Minister plans a whistle-stop charm offensive with EU leaders this week.
Thriller writer Anthony Horowitz is at the helm of the latest Bond book, which is based on an unfilmed Ian Fleming TV script.
Actress who plays iconic Daenerys Targaryen admitted she didn't want to become typecast for nudity.