Andrea Leadsom looks set to expand the “inhumane and ineffective slaughter” of badgers – despite scientists dismissing suggestions the policy helps control TB in cattle – in one of her first major acts as Environment Secretary, campaigners have said.

Ms Leadsom, who supports fox hunting, has backed selling off Britain’s forests and opposed measures to halt climate change, was appointed to the Cabinet post by Theresa May after dropping out of the Conservative party leadership race.

A string of eminent scientists have criticised the decision to cull badgers, with Professor David Macdonald, who chairs Natural England’s Science Advisory Committee, describing trials in 2013 as an “epic failure” in 2014.

In June last year, the Government admitted that only one of just four badgers tested for TB after they were killed during the cull actually had TB.

However, according to a report by the BBC, the culls are to be expanded into north and south Devon, north Cornwall, west Dorset and south Herefordshire. Culls, in which the badgers are shot, already take place in Dorset, Gloucestershire and Somerset.

The broadcaster spoke to a farmer who had signed up for the cull in one of the new areas.

The Department for Environment, Food and Rural Affairs (Defra) refused to confirm the report, but did not deny it and issued a response defending the use of “badger control in areas where TB is rife”.

However, the Royal Society for the Prevention of Cruelty to Animals (RSPCA) said in a statement it was “alarmed that despite three years of failed culls the UK Government is now forging ahead with plans to kill badgers in six different areas”.

David Bowles, the RSPCA’s assistant director of public affairs, said: “We are saddened but unsurprised at the restart of the badger culls, but to extend the number of cull areas further is alarming – especially when the last three years of culls have been such a failure, often missing targets such as numbers to be killed.

“This action is flying in the face of public and scientific opinion. We remain firmly opposed to plans for a widespread cull because we have not seen any evidence that the pilot culls have succeeded in reducing bovine TB in the cull areas and we have serious concerns about the humaneness of the culling methods used.”

And Paul Wilkinson, The Wildlife Trusts’ head of living landscapes, said the main way that cattle were infected with TB was from other cows, not badgers.

“The results of the previous badger culls indicate that this policy is flawed and unsupported by the evidence,” he said.

“Culling has been shown to be more expensive, less effective than other bovine TB control mechanisms and the free-shooting of badgers has been shown to be an inhumane method of killing.

“A vaccine for cattle should be a priority. The Government has failed to develop one for TB. UK cattle are already vaccinated for up to 16 diseases – why should TB be different?”

A study published earlier this year found that badgers deliberately avoided cattle, making direct transfer of the disease unlikely. But they like to forage for food on cow pastures, so could potentially pass on TB through the environment.

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Green MP Caroline Lucas urged Ms Leadsom to “think again” before “needlessly inflicting such harm on one of Britain’s best-loved wild animals”.

“These reports suggest that one of Andrea Leadsom’s first acts as Secretary of State at Defra is to oversee an extension to the inhumane and ineffective badger cull,” she said.

“Her decision to wave through this slaughter in our countryside shows a shocking disregard for animal welfare – and flies in the face of scientific evidence on the spread of bovine TB.”

And Rachael Maskell MP, Labour’s Shadow Environment Secretary, said: “We need a different approach based on what works, not this unscientific, unevidenced and ineffective Tory cull.

“It is time for long-term solutions to combat bovine TB and for the Government to prioritise the vaccine which is better for all animal welfare and a solution that is proven to work.”

In September last year, eminent scientists including Professor John Krebs, formerly president of the British Science Association, wrote an open letter to the Guardian calling for an end to badger culling. They wrote that experts had concluded culling made "no meaningful contribution to cattle TV control in Britain" after a Government-funded, £50m study over 10 years.

Ross Murray, president of rural business and landowners group the CLA, said: “We support the Government’s 25-year strategy for eradicating bovine TB. The badger cull is one important part of a comprehensive strategy which also includes pre and post movement testing of cattle, the removal and slaughter of infected animals and vaccination.

"Bovine TB is a devastating disease that is causing misery for dairy and livestock farmers across the countryside. It is vital that all those involved in the cull have the support of local people and law enforcement as they carry out this important task. We are grateful to all those that are taking part in this important effort and call on all those who value the English countryside to continue supporting our UK farmers and their herds.”

The National Farmers Union declined to comment, saying it was "speculation" until the actual announcement was made by the Government.

A Defra spokesperson said: “Natural England is currently considering applications for further badger control licences as part of the usual licencing process.

“England has the highest incidence of TB in Europe and that is why we are taking strong action to deliver our 25-year strategy to eradicate the disease and protect the future of our dairy and beef industries.

“Badger control in areas where TB is rife is one part of our long-term plan, which also includes strengthening cattle testing and movement controls and improving biosecurity on farm and when trading.