The Competition and Markets Authority has provisionally found that the trio, who account for about 90% of UK rolled lead supplies, entered into a cartel.

It alleges that the cartel colluded on prices, exchanged commercially sensitive information and avoided targeting some of each other’s customers.

Following an 18-month investigation, the firms are also accused of collectively refusing to supply another company whose business threatened to disrupt their market carve-up.

The suppliers named are: Hoddesdon headquartered Associated Lead Mills and its sister company Jamestown Metals; Welwyn Garden City-based H.J. Enthoven – trading as BLM British Lead – and Chester-based Calder Industrial Materials.

Michael Grenfell, the CMA’s Executive Director for Enforcement, said: “After a thorough investigation, the CMA has today provisionally found that these three companies colluded among themselves to share out the market.

“The CMA hopes that this provisional finding will send a strong reminder that companies need to follow competition laws. These are crucial to protecting customers from paying more for products than they should do.”

The CMA’s findings are, at this stage in its 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. Investigators will carefully consider any representations made before issuing final findings as to whether the law has been broken.