United Utilities at Manchester Crown Court

Keith Haslett, Wastewater Network Director at United Utilities, said: "We are investing £6bn in the North West over the five years to 2020 and making major environmental improvements, but we failed in our responsibility on this occasion. We apologise to our customers because we do care, both personally and professionally.

"The incident was caused by a faulty control valve at our wastewater facility in Oldham. The valve door failed, due to a worn drive nut.

"In the three years since the incident we have upgraded alert systems, introduced new alarm procedures and enhanced the control valve. We are investing a further £50 million in improvements along the River Medlock.

"We hope that customers will be encouraged that our overall performance has improved considerably since 2014, something the Environment Agency has recognised by awarding us “Industry Leading” status in its most recent assessment.

"We are proud of our partnership with environmental groups across our region, and continue to work with them to improve rivers and the local environment. This fine will be paid by shareholders and not customers".