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
The move has been criticised as political as it takes place amid a global health pandemic which has ravaged the country’s prisons.
The killing spree was the deadliest in New Zealand’s modern history.
Monday’s front pages feature a range of political and pandemic-related stories.