Badger culls were "ineffective" and caused far too much suffering of too many animals, an independent study has warned.
Research commissioned by the Government found that the number of badgers killed in Somerset and Gloucestershire fell short of targets set to limit the spread of TB in cattle.
More than 5% of badgers took longer than five minutes to die, failing the test for humaneness, according to the BBC.
The Independent Expert Panel was appointed by the Department for Environment and Rural Affairs to evaluate the pilots.
Marksmen were brought in to shoot the animals at night, with the aim of killing at least 70% in cull areas within a six-week period.
The duration was extended after initial figures suggested that just 58% of badgers were eradicated in the Somerset scheme and 30% in Gloucestershire.
However, the independent panel is reported to have found that less than half of badgers were killed in both areas during the first six weeks.
Defra had also agreed that the standard for declaring the culls humane would be 95% of the shot badgers dying within five minutes.
But the expert group has apparently concluded that between 6.4% and 18% of animals exceeded that limit, depending on the assumptions made.
No date has yet been set for the report to be published.
Leading activist Brian May said: "We should also mention that the report discovered that it was very inhumane as well. I don't think people will stand for this. You're talking about badgers taking five or 10 minutes to die.
"Owen Paterson's denied that but it's obviously true."
The guitarist with rock band Queen told BBC Breakfast that he had "a lot of sympathy for farmers", but added: "This is not the way to solve the problem. The way we believe we can solve it is by vaccinating the badgers, and also vaccinating the cows."
May said badgers can be vaccinated for "about £120 a head", and added that it has "just cost £4,200 per badger to kill the poor things".
Robin Hargreaves, president of the British Veterinary Association (BVA), said: "It is important to remember that these culls were pilots precisely because the Government needed to test the humaneness, safety and efficacy of controlled shooting as a method of culling badgers.
"Indeed, BVA called for controlled shooting to be tested and critically evaluated before it was rolled out.
"We are unable to comment in detail on the findings of the IEP until we have seen the report and had time to review all of the information but, if these figures are true, then they would certainly raise concerns about both the humaneness and efficacy of controlled shooting.
"We will look at the published report in detail and consider BVA's position in light of the IEP's findings.
"We have always stated that if the pilots were to fail on humaneness then BVA could not support the wider roll-out of the method of controlled shooting."
Dominic Dyer, chief executive of the Badger Trust and policy adviser to animal charity Care For The Wild, which has campaigned against the cull, said: "Anyone who has scrutinised the disastrous badger culls will have hoped for, and expected, an independent report to come up with this result - that the culls failed completely on both efficiency and humaneness grounds."
He called on Prime Minister David Cameron to intervene to stop the cull, which he said had been introduced for political, not practical, reasons.
He said the pilot culls had probably cost more than £10 million, or £4,000 per badger, and could increase the risk of TB in cattle as badgers moved around more following culling. Shooting of free-running badgers in the cull had been shown to be a failure, he added.
He also said many badgers could have been left to die long painful deaths as a result of a lack of effective monitoring for humaneness.
"The badger cull pilots have been a complete failure on scientific, economic and animal welfare grounds, and now the independent expert panel has reached this conclusion, all future plans to cull badgers should be stopped immediately," he said.