Water companies could face a spate of legal challenges by people and businesses affected by sewage pollution after a ruling that United Utilities could be sued by a private company for damage caused by the dumping of human waste.

Lawyers said it was a “watershed moment” as the courts had previously ruled that penalties for water companies were a matter for the regulator, and companies could not sue firms for damage caused to their property by sewage pollution.

The Manchester Ship Canal Company, which has been trying since 2010 to bring a claim against United Utilities, has alleged that discharges from 121 sewage outfalls within its networks constituted a trespass.

In February 2012, the high court ruled in favour of United Utilities, but this was later overturned by the court of appeal, and then restored by the supreme court in 2014. Then, in March 2021, the high court ruled it was the role of regulators and not the courts to address problems caused by sewage dumping.

The Environmental Law Foundation, supported by the Good Law Project, challenged this decision, arguing that there should be legal options for people directly affected by sewage pollution. But the court of appeal found against them and said the only option for recourse in issues caused by pollution was through the regulator, and that the law did not allow people or companies directly affected to bring private claims against the water companies.

The case then went to the supreme court, which overturned the previous rulings and found that United Utilities can be held to account for damage caused by discharges.

The court said the 1991 Water Industry Act does not prevent the company from bringing a claim for nuisance or trespass when a canal is polluted by sewage discharges from United Utilities’ sewers, even if there has been no deliberate misconduct or negligence.