There has been angry reaction to the resumption of the badger cull to try to stop the spread of bovine TB in cattle.
It comes as two pilot schemes start for the second year in Gloucestershire and Somerset.
ITV News' Rupert Evelyn reports.
People against the controversial badger cull have reacted angrily to news the Government is testing gassing as a potential method for killing badgers.
Farmers and ministers say culling of badgers is necessary to tackle bovine TB in livestock, but opponents say it is inhumane, ineffective and should be abandoned in favour of tougher cattle measures and vaccination.
Tests using carbon monoxide have been conducted since last summer, although no animals have been involved in the trial, an FOI request found.
"Gassing could cause considerable animal suffering", veterinarian Mark Jones, executive director of Humane Society International UK, said.
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.
Pilot badger culls in Gloucestershire and Somerset will continue this year, but the scheme will not yet be rolled out to other areas, Environment Secretary Owen Paterson has announced.
An RSPCA advert suggesting that badgers in cull areas would be "exterminated" has been banned following 119 complaints.
The ad featured an image of a syringe and bullet at the top of the page with a headline reading "Vaccinate or exterminate?" before text continued: "The UK government wants to shoot England's badgers. We want to vaccinate them - and save their lives."
Conservative MP Simon Hart, the Farmers' Union of Wales, Welsh Conservative AM Antoinette Sandbach and 116 members of the public complained about the ad, with most saying the term "exterminate" was inaccurate and alarmist.
The RSPCA said the word "exterminate" was used carefully and deliberately, saying it had "a literal meaning of total eradication and a common use meaning of killing on a massive scale".
The Advertising Standards Agency said: "...Consumers were likely to interpret the claim, along with the text 'The UK government wants to shoot England's badgers', to mean that all badgers would be eradicated in the cull areas. On that basis, we concluded the claim was likely to mislead."
It ruled that the ad must not appear again in its current form.
The Government has been forced to cancel the controversial badger cull after marksmen failed to kill enough of the animals.
One Tory MP suggested that the badgers may have been staying underground because the weather had "gone cold".
ITV News' Ben Chapman reports.
The Government's badger cull policy has been dealt a further blow by the failure of another trial to kill sufficient animals.
Shooting will be halted in Gloucestershire tomorrow at 12 noon - three weeks before schedule - after it became clear even a reduced target would not be met.
The pilot scheme was extended by eight weeks after marksmen exterminated only around 30% of the local badger population - well short of a 70% target.
Natural England said it had pulled the plug as the cull was set to miss a revised level of 58%.
Environment Secretary Owen Paterson said the chief veterinary officer has advised that the period of culling badgers should be extended in Gloucestershire.
In a written statement to Parliament, Mr Paterson said the cull has killed 708 of an estimated 2,350 badgers in the county - less than 30% of the total rather than the 70% that had been planned.
Mr Paterson said an application is being considered by Natural England.
He told the House of Commons that early indications showed the culls in both Gloucestershire and neighbouring Somerset were carried out in a "safe and humane" way, but demonstrated that "the cull period may need to be longer than six weeks in future".