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."
Princess Anne has explained why she supports genetically modified crops - despite her brother Charles being an outspoken opponent of them.
"They do add to our ability to perhaps be more efficient users of the land," she told BBC One's Countryfile.
"I think in the long-term, when you've got the prospect of nine billion [people] to feed, you are going to need some help in doing that."
Prince Charles once warned that the development of GM crops risked creating "the biggest disaster environmentally of all time" and accused multinational corporations of conducting an experiment with nature which had gone "seriously wrong".
Princess Anne has suggested that Britain should eat more horsemeat to stop surplus animals being abandoned and said she thinks the food tastes "very good."
"An awful lot of the abandonments is because they don't perceive there to be any value in the animals," she told BBC One's Countryfile.
"The meat trade adds value to the animal so there is some point in keeping it healthy if it's got an end point that it can go to."
Asked if she had ever eaten horse meat, she replied: "Oh, certainly."
She described the meat as tasting "very good, actually."
Princess Anne has said that gassing badgers would be the most humane way to cull the animals.
The Government is considering introducing gassing after a report said that shooting badgers would not bring their numbers down enough to stop them spreading tuberculosis in cattle.
"Most of the people who did it in the past will tell you that gas is a much nicer way of doing it, if that's not a silly expression," she told BBC One's Countryfile.
"How it works is that you go to sleep, basically."
The royal owns a heard of around 30 cattle and has lost 15 rare white park cows to bovine tuberculosis in the last two years.
Gassing badgers is "the most humane way" to control their numbers, Princess Anne has said.
The Government is considering introducing gassing after a report said that shooting the animals would not bring their numbers down enough to stop them spreading tuberculosis in cattle.
"If we want to control badgers, the most humane way of doing it is to gas them," the Princess Royal told the BBC's Countryfile programme.
Campaigners have backed the Princess Royal for challenging the development of large-scale new towns and instead highlighting the benefits of limited expansion of rural villages.
The Campaign to Protect Rural England welcomed her intervention, saying it was important to have a "living countryside" with villages which grew "organically".
Princess Anne has advocated small-scale developments in villages, rather than 'big estates' as a solution to the rural housing crisis, according to The Telegraph.
Speaking just weeks after the Coalition discussed plans for two new garden cities, the Princess Royal entered the debate over Britain's housing shortage by asking planners if it was "really necessary" to build developments of up to 15,000 new houses.
Instead, small developments of between six and 12 homes could be scattered villages to make up the same number, she said.
She said: “Our battle is to argue the toss with real house builders that this has real value - and some local authorities, frankly, who would much rather invest in a large scale development.
“Maybe it isn't such good value if you have to build in the facilities that need to go with it".
The owner of a horse sanctuary in Staffordshire has hit back at a suggestion from Princess Anne that eating horsemeat would improve the welfare of the animals.
Billy Wilson likened it to "cannibalism" as he said horses are the "closest animals to mankind".
Yesterday Princess Anne wondered if the UK should be considering creating a market for horsemeat to stop the animals being abandoned in increasing numbers.
Today one butcher claimed the British attitude towards eating horses is unique among our European neighbours.
And as Damon Green reports, as the debate continues, there will be more horses needing to find a home.
Princess Anne has suggested that people in Britain should consider eating horsemeat because it would improve the welfare of the animals.
She said that "Our attitudes to the horsemeat trade may have to change," because those in the trade "value their horses and look after them well".
The Princess asked whether we "should we be considering a real market for horsemeat and would that reduce the number of welfare case?"
"I think this needs a debate."
The Princess Royal, who is President of the charity World Horse Welfare, was speaking at its annual meeting when she made the comments, The Telegraph reported.
Two university students have claimed they were "assaulted" by staff and detained for nearly six hours by police ahead of a visit by the Princess Royal.
Hona-Luisa Cohen-Fuentes and Euan Kidston claimed they were studying in the University of Edinburgh on Tuesday when they were "roughly seized" by staff and told: "We have someone really important coming here, we can't have the likes of you roaming around."
The students allege they were then prevented from leaving by staff who said they "could be any random scum off the street".
University chiefs say the students "could not provide a satisfactory explanation" for their presence in a restricted area, which was being prepared for Anne's visit.
A Police Scotland spokesman said: "During a security check at an Edinburgh University venue two people were found within a restricted area and were subsequently detained. They were later released without charge."