The firm admitted the offence before Sunderland magistrates and was also ordered to pay costs of £1,960 to the Environment Agency (EA), which brought the case.

Trevor Cooper, prosecuting for the EA, said that on April 11 last year officers had received a call from a member of the public to inform them that Coop House Dene Burn at South Hetton, County Durham, was polluted.

This stream runs through Coop House Wood and is a popular spot for dog walkers.

They discovered that the stream was seriously polluted with sewage, after a blockage in a sewer overflow.

Dead animals were found more than two miles from the source of the pollution, which said to have been evidence of significant damage to the aquatic ecosystem.

Northumbrian Water had an alarm system fitted on the sewer overflow, but the technology had failed.

In mitigation, the company entered an early guilty plea and had fully co-operated with the EA during its investigations.