A secret government trial to see how effective it would be to 'gas' badgers in their setts has been called 'scandalous' and a sign of desperation, despite no live badgers being used.

The Guardian revealed yesterday that secret government trials of gassing badger setts have been underway since the summer of 2013, according to documents released under freedom of information rules.

The tests, at an undisclosed location, are examining how the poisons carbon monoxide and nitrogen oxide flow through complex badger setts. No animals or active badger setts have so far been involved in the tests, which are ongoing and have no end date.

Farmer-led pilot culls have failed to kill the target numbers of badgers and was not judged sufficiently humane by an independent panel.

Defra has said there will be "some preliminary tests to investigate the dynamics of CO dispersal in a sett environment to determinate whether any available delivery mechanisms have the potential to achieve humane and effective outcomes in real sett situations".

Adding clearly that "this will not involve tests on live animals.”

According to the Humane Society International previous studies assessing gassing saw "cats, dogs, guinea pigs and monkeys enduring anything from tremors and vomiting to severe lung pain, heart attack, suffocation, coma and death".

Caroline Allen, the Green Party's animals spokesperson, and a working vet, said: “I am horrified, although not surprised, that the Government is pursuing ever more desperate ways of killing badgers as part of their fundamentally flawed approach to the problem of bTB.

“It is outrageous that Defra are using our public money in their obsession with finding ways to kill badgers. Especially when this method has already been tested and has been found to be so inhumane it was banned.

“Research has already shown that gassing badgers in their setts is inhumane because of difficulties achieving lethal concentrations of gas rapidly throughout complex badger setts. Badgers who don’t immediately succumb die a lingering death, or are left with brain damage. And cubs are less affected by the gas, so can be left orphaned to die of starvation.

“Sett gassing is indiscriminate and research has also shown it could impact other animals in or near targeted badger setts, which could potentially include some endangered species.

“All the independent experts agree that tackling the issue of bTB needs to be about cattle controls.

“Badger gassing must be stopped and I will be campaigning with fellow vets, Greens and animal lovers to help this happen.”