United Utilities has been accused by the BBC of downgrading sewage incidents to improve its performance on dumping.
In a Panorama documentary, the northwest utility is alleged to have downgraded 60 incidents so they did not count in official figures.
Regulator Ofwat rated United Utilities’ performance as the best in the sector last year at 126 pollution incidents graded 1-3 for their seriousness, though category 4 spills that are deemed to have no environmental impact are not included.
FTSE 100-listed United Utilities received a £5.1 million bonus based on its performance, which it can take from customer bills over the next year.
One of the sewage discharges reportedly downgraded was into the middle of Lake Windermere, a globally renowned beauty spot in the Lake District.
Originally believed to be a category 2 incident, United Utilities reportedly downgraded the incident.
In a statement, the company said: “Panorama has made a series of allegations about United Utilities, which we strongly reject.
“Pollution incidents are investigated and action taken where necessary.
“The Environment Agency, as the regulator, determines both the initial and final categorisation of pollution incidents.”
Insiders quoted in the documentary said that the Environment Agency visited only six of 931 reported pollution incidents in the last three years and allege it routinely fails to check spillages.
An Environment Agency spokesperson said: “We take our responsibility to protect the environment very seriously and will always pursue and prosecute companies that are deliberately obstructive or misleading.
“In the last six years, we have pursued four successful criminal prosecutions against United Utilities and required the company to pay millions to environmental charities to put right the cause and effects of their offending.”
Shares in United Utilities fell 2.6% to 1,063p.