A significant number of livestock farmers are thought to be involved in the illegal killing of badgers. Farmers jaded by the Welsh government's change of heart over a proposed badger cull in the country's Intensive Action Area, which came following a review of the scientific evidence surrounding culling, are thought to have taken the law into their own hands and begun killing badgers.

Researchers from Bangor University said randomised response technique (RRT), a little-used method for estimating how many people are involved in sensitive or illegal activities, has provided information on the level of badger persecution in Wales. Working with colleagues at the universities of Kent and Kingston, the researchers were able to make an estimate of the rate of illegal badger killing.

They suggested that over 10 percent of livestock farmers in Wales illegally killed badgers in the 12 months leading up to the study, though they allowed a 5 percent margin for error. The researchers spoke to 428 farmers at rural shows in Wales; they said the proportion of the farming community interviewed is higher than in other such polls.

The researchers said that in addition to the illegality of the actions, and animal rights issues, such killing may be exacerbating the spread of bovine TB to livestock, the pretext under which much badger persecution is being carried out.

Dr Paul Cross, from Bangor University's School of Environment, Natural Resources & Geography said, "The proportion of farmers estimated to have killed badgers should be considered by policy makers and in the wider debate. Intensive badger culling is one approach being considered by policy makers [in England], in an attempt to control the spread of tuberculosis in cattle. However, studies investigating the effects of badger culling on TB outbreaks in cattle have not factored in the prevalence of illegal badger killing, and its potential to spread disease."

Commenting on Thursday, Badger Trust spokesperson Jack Reedy said the findings were "depressing." He said, "It's a sad day. This [activity] really is flying in the face of science; if blind prejudice continues to hold sway, then this killing could be doing irreparable harm in the long run.

"If there is infection in badger populations being persecuted, then disturbing these communities could increase the proportion of infected badgers overall. This has been known since the early noughties and has been said over and again - you can't blast on as if it's the 19th Century."

Mr Reedy added that the Randomised Badger Culling Trials, conducted under the previous government, which accounted for much of the evidence examined by Defra and the Welsh Government ahead of their decisions on badger culling, showed that reactive killing was "dangerously counter-productive. So much so that trialling the method was stopped – the risk was simply too high."

Reinforcing the study's value as the first to look at levels of unsanctioned reactive killing, a spokesperson for the National Wildlife Crime Unit told Farming Online that evidence of such illegal killing is sparse and that very little is known officially about levels of persecution. The spokesperson said, "We have nothing in our data to suggest that badger persecution is happening on this scale, though we don't have any evidence that would negate the findings either. We know there is a history of badger persecution in South Wales and issues of persecution tend to be reported to the RSPCA before they are referred to us."