Liz Truss is responsible for farmers being allowed to dump a catastrophic “chemical cocktail” of pollutants into Britain’s rivers, according to environmental campaigners.

This has meant agricultural waste now outstrips sewage as the leading danger to England’s waterways.

Liz Truss at a farm in Newton Abbot, Devon earlier this month.

Truss boasted of cutting farm inspections in a parliamentary exchange in 2015 when she was environment secretary. This allowed farmers to dump waste, including pesticides and animal faeces, into rivers.

“We have seen a reduction of 34,000 farm inspections a year and an 80% reduction in red tape from Defra [Department for Environment, Food and Rural Affairs]. That is vital for our £100bn food and farming industry,” Truss, who held the environment post from 2014 to 2016, told parliament.

“A future Conservative government would continue to bear down on red tape. We are considering pilots for landowners and farmers to manage watercourses themselves, to get rid of a lot of bureaucracy.”

Because of cuts to the Environment Agency and Truss’s policy of trimming official rules and inspections, farmers were able to dump waste in their local watercourses without much fear of being caught and fined. Campaigners say this has had dire consequences for England’s rivers.

For example, in the Wye valley, home to one of Europe’s largest concentrations of intensive livestock production, Lancaster University found there were 3,000 tonnes of excess phosphorus caused by agriculture seeping into the valley’s waterways.

Other rivers polluted by agriculture include the Axe, which flows through Dorset, Somerset and Devon, the Derwent in Yorkshire, the Ehen in Cumbria, and the Test and Itchen rivers in Hampshire.

Louisa Casson, head of food and forests at Greenpeace UK, said: “Letting industrial farms unleash a chemical cocktail into our rivers and get away with it has been catastrophic for our environment. Liz Truss’s crusade against red tape has been a key contributor and, ultimately, our wildlife and the public have been left wading through the resulting filth in the rivers they cherish.”

The Guardian revealed last week that Truss presided over huge cuts to the Environment Agency’s sewage monitoring system. She implemented a £24m cut from a government grant for environmental protection – including surveillance of water companies to prevent the dumping of raw sewage – between 2014-15 and 2016-17, according to the National Audit Office.

During Truss’s tenure at Defra, the department was taken to court by Fish Legal and the WWF over a change to the voluntary reporting of farm waste dumping. After a judicial review, the Environment Agency inspected the river Axe. It found that from the winter of 2016, 95% of farms had not complied with slurry storage regulations and 49% were polluting the river.

A spokesperson for the Wildlife Trusts explained: “Clearly, cutting farm inspections has left a legacy of significant water pollution.”

Campaigners say Truss’s policy meant that farm visits dwindled for years, and in 2018-19 inspectors visited only 403 farms to check for activities and practices that could cause water pollution. There are 106,000 registered farm businesses in England. Campaign group WildFish calculated that at that rate, farms could expect an inspection every 263 years.

Following the cuts in inspections, by 2019 agriculture had overtaken the water industry as the sector responsible for the greatest number of failures against water targets.

“Farm inspections are not designed to catch farmers out,” said Ali Morse, water policy manager at the Wildlife Trusts. “They ensure that our rivers and seas aren’t polluted, and that valuable soils and nutrients stay in fields and out of rivers. This is in the interests of the farming sector as much as our environment.”

Liz Truss was contacted but declined to comment.