Lynda and Richard Whittemore bought Quennells farm, in the quiet Sussex countryside, six years ago. They hoped to lead “an idyllic lifestyle”, tending their flock of 400 pedigree, grass-fed Lleyn sheep and 45 Highland cattle on 180 acres of farmland.

“We have an undulating field at the back of the stream, winding to the other corner", said Lynda. "Usually it has lovely clear water, with a gentle slope down to the water supply. It’s picturesque...they don’t need troughs, they can walk down to drink the water.”

Next door to their farm was another: Crouchland. But this farm was not a small-scale, pedigree operation like that of the Whittemores. Crouchland is an intensive dairy farm which also processes large amounts of manure, turning it into biogas.

By 2013 it had installed an industrial-size anaerobic digester - government-subsidised machinery which turns food and agricultural waste into gas which can be sold to the national grid. It began processing waste from 20 local farms and built extra slurry vats in order to store the byproducts.

In March 2015, Lynda explained, there was a “nasty spill of digestate” - a toxic mix of manure, water and chemicals - linked back to Crouchland farm. It polluted 70 acres of Quennells farm land. “Thick, black smelly tarry stuff flowing down our stream," she said. "It was chugging along, killing little frogs, fish and invertebrates. They were wiped out.”

Such an occurrence is far from a one-off case. A Bureau investigation has found pig, poultry and dairy farms are releasing harmful pollution once a week on average in England and Wales.

We have documented dozens of instances of manure pouring into waterways, carcasses being illicitly dumped and noxious fumes being emitted, among other infractions - all of which can seriously damage ecological systems, and are often against the law.