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.
British scientists have applied to begin field trials of a genetically modified crop containing fish oil nutrients in its seeds in what could be a big boost to the fish farming industry.
An application to conduct the trials at Rothamsted Research agricultural institute has been submitted to the Department for Environment, Food and Rural Affairs (Defra) and is expected to begin from April if endorsed.
The scientists are bidding to produce the world's first sustainable plant source of fish oil omega-3 fatty acids by "cutting and pasting" genes taken from marine algae, which could help protect against heart disease.
While the fish farming industry, which consumes 80% of fish oil supplies, stands to benefit from the trials, in the long term the GM-oil could also be included in food products like margarine.
The Prime Minister has come under renewed fire over flood defence spending after it emerged that figures showing increased funding include money committed by the last government.
David Cameron told the Commons last week that "in this current four-year period, we are spending £2.3 billion, compared with £2.1 billion in the previous period" on flood defences.
But the current four-year period dates back 2010/2011 - the last year of spending commitments made under Labour when money for flood management reached a high of £664 million, before being reduced from 2011/2012 as part of the Coalition's spending cuts.
Analysis by Friends of the Earth suggests the Government is spending £2.32 billion in the current spending review (2011/12-2014/15) period, slightly less than £2.366 billion in the previous four years.
The Government said Defra's spending on flood defence would increase in real terms in the coming years despite budget cuts.
Environment Minister George Eustice told the BBC Radio 4 Today programme:
We within Defra have prioritised spending on flood defence in difficult times, when budgets across Government are having to be cut.
We've maintained spending on flood defence specifically and we are going to spend around £2.3 billion between 2015 and 2021, which will be an increase in real terms.
So we are committed to constantly keep improving our defence infrastructure when it comes to flooding.
Flood defences have held despite taking "a real battering" over the last few weeks, the head of the environment, food and rural affairs committee has told Daybreak.
Anne McIntosh implied the taxpayer could take some small comfort that "flood defences have held in every scenario in these last few weeks", especially after the Environment Agency had its budget slashed as part of the austerity programme.
However, she warned what little money was available would have to go on maintaining existing flood defences if Britain was to withstand storms in the future:
"They will need to be maintained, so it is not just a case of building new homes in appropriate places....but maintaining those flood defences that have served the country so well in this battering that we have seen over the last few days."