Water and sewerage companies, including Thames Water, are set to be hit with a new class action after law firm RPC issued a formal letter notifying of the legal proceedings.

The law firm issued letters before action on its opt-out competition collective action to Severn Trent, United Utilities, Yorkshire Water, Thames Water, Northumbrian Water and Anglian Water.

The new claim alleges that non-household customers have been overcharged on their water bills as a result of each water company’s infringement of competition laws through the under-reporting of sewage spills.

This claim is said to be made up of as many as one million non-household customers, which includes businesses, charities and local government, with damages of up to £510m being sought.

This is the second class action against these six English water and sewerage companies.

Another lawsuit was launched to the Competition Appeal Tribunal (CAT) last year on behalf of household customers by partner Zoё Mernick-Levene, who at that time, was at law firm Leigh Day.

That case was at a collective proceedings order hearing back in September, for which a decision is pending by the Tribunal.