Officials at the Competition and Markets Authority (CMA) have been investigating M.G.F. (Trench Construction Systems) Ltd, Vp plc and Mabey Hire Ltd.

The CMA said it “has provisionally found that the three businesses formed a cartel to reduce competition and keep prices up.

“This involved sharing confidential information on pricing and commercial strategy and coordinating their commercial activities.”

An investigation was launched in 2017 when Mabey blew the whistle and approached the CMA.

Mabey has confessed its role and will not be fined in accordance with the CMA’s leniency programme.

Groundworks products include braces, props and sheeting and are used to protect excavations on a wide range of major building and civils developments, railway line works and water pipe upgrades.

Michael Grenfell, the CMA’s Executive Director for Enforcement, said: “These are three major suppliers of equipment used to keep construction workers safe.

“It is crucial that builders and their customers benefit from genuinely competitive pricing for this essential equipment.”

The CMA added: “Findings are, at this stage in the investigation, provisional and do not necessarily lead to a decision that the companies have breached competition law.

“The firms now have the opportunity to consider the detail of the CMA’s provisional findings and respond to it.

“The CMA will carefully consider any representations made before issuing its final findings as to whether the law has been broken.”

In a stock exchange statement Vp said: “Vp is reviewing these provisional findings and will continue to cooperate fully with the CMA.  The Group will make further announcements as appropriate.”