Natural England and MPs are urging the government to change its livestock rules to stop ponies on Dartmoor from being culled.

Semi-wild ponies have roamed Dartmoor for more than 4,000 years and have become uniquely suited to the boggy landscape, providing a charming sight for those who visit the national park.

There was therefore widespread outrage after reports that government quango Natural England were going to cause a cull of up to 90% of the ponies, with the Conservative party calling for the government body to be reviewed and possibly stripped of its powers.

However, sources at the quango say it is the Department for Environment, Food and Rural Affairs’ (Defra) policy that is at fault, as it fails to differentiate between sheep and ponies. Because the barren moors are so overgrazed, putting species including rare birds and butterflies at risk as there is no food or nesting sites for them, Natural England said there should be an aim to destock the moors by 76%.

Natural England has no powers to order a cull of either sheep or ponies. But commoners on the moor are currently paid for their stewardship of the national park. Evidence has found that overgrazing, mainly by sheep, has prevented wildflowers and other plants from growing and emptied parts of Dartmoor of nature.

New government plans say that in order to access these funds, those who graze animals on the moor will have to reduce their livestock numbers, leading to some animals being culled.

However, sources at Natural England said the rules, drafted by Defra, make no differentiation between sheep and ponies. While sheep eat the most nutritious and desirable plants, horses are highly effective at stripping the moor of tough, unpalatable vegetation such as molinia grass and gorse, both of which are swamping the peat bogs and heather of the moor. Farmers are much more likely to get rid of ponies than their sheep, as they can sell the latter for meat.

A source said: “Defra policy in agri-environment schemes does not allow us to differentiate between livestock animals in making agreements.” Sources at the quango said this had been deeply frustrating. Online abuse directed at Natural England included X posts that claimed its chair, Tony Juniper, wanted to personally kill ponies.

There are fewer than 1,000 Dartmoor hill ponies, down from around 7,000 in 1999, according to the Dartmoor Hill Pony Association. A government commissioned review into Dartmoor, published two years ago, found that Natural England “should not take actions likely to result in a reduction in pony numbers”, adding they were “invaluable for conservation grazing”.

Joss Hibbs, secretary of the DHPA, said: “Natural England is putting ponies in direct competition with commercial livestock who pay the farmers’ bills. Their plans disregard the scientific evidence and could decimate an endangered species that has been a feature of the landscape for over 4,500 years.”

Natural England and MPs are calling for Defra to give a carve-out for the ponies. Local Labour MP Steve Race said: “The ponies are not livestock – they’ve existed as an integral part of Dartmoor’s ecosystem for thousands of years, and are the only thing that eats the highly destructive molinia grass that is reducing Dartmoor’s biodiversity.”

Race, who’s constituency is in nearby Exeter, and the other Devon MPs are meeting with ministers at Defra next week to discuss the carve-out.

Caroline Voaden, the Liberal Democrat MP for South Devon, whose constituency covers part of Dartmoor, said: “Dartmoor ponies have roamed the moors since the bronze age, yet under plans drawn up by a government quango, their population could drop by as much as 90% in the next few years. I am deeply alarmed, as are many others, that we might see the near elimination of ponies on the moor. The potential consequences of Natural England’s proposed grazing contracts are staggering. We must do everything we can to protect what are among the last semi-wild species of pony in the UK and ensure their survival for generations to come.”

Defence minister and Plymouth MP, Luke Pollard, has written to Defra to ask that ponies are given a carve-out. He said: “I am deeply concerned that the proposed contracts include ponies within overall livestock unit limits, which risks creating a financial incentive to prioritise more commercially viable livestock, such as cattle and sheep, over ponies.”

Kemi Badenoch, the leader of the Conservative party, said: “This is total madness from another unaccountable quango. The government must overrule Natural England and stop it immediately.”

A spokesperson for the prime minister said: “This government will not allow a cull of Dartmoor ponies and we don’t manage our pony populations by culling in this country.”