Water firm United Utilities has launched a £25m High Court legal action against contractor Alfred McAlpine and designer Degremont over problems on a water treatment plant in Liverpool.

United Utilities has argued that local residents are threatening to sue for damages because of smells and substances that are leaking from the plant as a result of its defective design.

The High Court writ said that Dunstable-based Degremont, which designed the plant and supplied materials and equipment, is being sued.

United Utilities is also suing Biwater Treatment and Alfred McAlpine Construction, trading as Biwater-Alfred McAlpine Joint Venture, for their part in building the plant, which was completed four years ago.

The writ claimed that Degremont had wrongly stated there would be no odour from the filter bed, and induced United Utilities – formerly North West Water – to enter into a complete design package through misrepresentations and negligent misstatements. The writ said that Degremont breached the contract and its design was defective and inadequate.

United Utilities is suing Degremont for damages for breach of contract, and liquidated damages for failure to complete the contract on time. It also seeks an indemnity against claims brought by residents.

The writ claimed that the plant had never worked properly

The writ claimed that the plant had never worked properly as a result of breaches of contract by the two companies that built it. It also claimed that the plant had failed to comply with statutory requirements.

United Utilities has accused all three companies of failing to provide guarantees from their parent companies, in breach of contract.

A spokesperson for Alfred McAlpine said: “We will defend our position rigorously.”

Degremont and United Utilities both refused to comment on the action.