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
A son paid off his parents' mortgage for Christmas - reducing them to tears.
Intruders killed an eight-week-old puppy during a failed attempt to steal from a house in East Lothian, police have said.
It will be a cold day today, with temperatures dipping below freezing shortly after dark.