Government advisers are being accused of allowing caged badgers to die of thirst or heat stroke as a badger cull is carried out in this week’s record temperatures.

Campaigners are stepping up pressure on environment secretary Michael Gove to cancel licences extending the cull into new areas, because of the heatwave.

They fear that animals trapped during the official cull across hundreds of acres of countryside are being left for hours on end in the sun, with no water.

With temperatures having reached up to 33C in some areas of England, wildlife activists believe Natural England, the government advisory body that issues cull licences, is failing to enforce its own guidelines on the cull, which say marksmen must suspend trapping if animals would be exposed to extremes of weather.

The Badger Trust has written to Natural England chiefs calling for an immediate halt to trapping, saying that in temperatures of 30C or more it is inhumane.

“This is a serious animal-welfare issue. We are likely to see hundreds of badgers trapped in cages in blazing hot sunshine with no access to water or shade – it’s horrendous,” said Dominic Dyer, head of the Badger Trust. “The supplementary cull licences should be revoked.”

This summer cull zones were extended to include many areas of England at risk of having bovine tuberculosis outbreaks. In West Gloucestershire and West Somerset in particular trappers have been out laying cages baited with peanuts, one of badgers’ favourite foods.

They typically set the traps in remote locations during the daytime then return the following morning to check them.

This means mammals could be caged for more than 12 hours. As the earth is rock-hard from weeks without rain, badgers cannot dig for earthworms, their usual diet.

“Contractors are out laying cages in hidden areas and no one is checking on them because checks weren’t in the free licence conditions,” Mr Dyer said.

As the heatwave is forecast to mean temperatures of up to 34.5C this week, badgers will slowly die of dehydration or heat exhaustion, exacerbated by the afternoon and early-morning sun, he predicts.

“The contractors are poorly paid, the cull is uncontrolled, unregulated and in these conditions it’s breaking both the guidelines and animal-welfare laws. Natural England is making no allowance for the extreme conditions.”

The Animal Welfare Act 2006 makes it an offence to cause unnecessary suffering to any animal.

The heatwave has left badgers desperate for food, with many cubs found to be undernourished, Mr Dyer said, adding: “Downing Street are worried that images of badgers dead from heat exhaustion in cages will soon appear in the media, which will not be good for Mr Gove’s animal-friendly reputation.”

The government has extended the cull of the mammals, in response to demands for action to eradicate TB in farm herds.

Last week environment minister George Eustice said in a parliamentary written answer that Natural England’s guidance must ensure culling is done “humanely”, “including reducing the risks that trapped badgers suffering exposure due to severe weather”. The body keeps this under review, Mr Eustice added.

The guidance also quotes the Animal Welfare Act, stating: “this includes a wild animal held in a trap”.

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A Natural England spokesperson said: “Badger control has been authorised in two areas so far this year as part of supplementary culling operations. Any further licensing decisions will be made later this summer.

“We publish a clear best practice guide to ensure culling is as humane as possible and contractors are trained to deploy cages within cover to mitigate against exposure to inclement weather (hot or cold).”