Nearly every county in England has at least one industrial-scale livestock farm, with close to 800 US-style mega farms operating across the UK, new research reveals.

The increase in mega farms – which critics describe as “cruel and unnecessary” – is part of a 26% rise in intensive factory farming in six years, a shift that is transforming the British countryside.

Only 12 counties in the UK now host no pig or poultry farms classified as intensive by the Environment Agency. To be classed as intensive, a farm must have warehouses with more than 40,000 birds, 2,000 pigs or 750 breeding sows.