The competition watchdog said it has provisionally found that the three firms broke competition law by coordinating prices for customers and sharing the market.

Two of the businesses – Derbyshire-based Stanton Bonna Concrete Ltd and Somerset-based CPM Group Ltd – have admitted to their part in the cartel, which started in 2006 and continued for almost seven years. A third company, FP McCann Ltd, headquartered in Northern Ireland, is also under investigation and has not made any admissions.

In a ‘statement of objections’ issued today, the CMA provisionally found that the companies held regular secret meetings to set up and operate an illegal cartel. Its aim was to fix or coordinate prices and share out the market for certain pre-cast concrete drainage products in Great Britain, with the intention of increasing prices and reducing competition.

These products are used in large infrastructure projects across Great Britain, including water management, roads and railways. Typical customers include engineering and construction companies; utilities providers; and local and national government.

Throughout the period of the alleged cartel activity, the companies were leading players, accounting for over half of the market. From 2010 onwards, they held over 90% of this market.

Michael Grenfell, executive director of enforcement, said: “Cartels damage competition and lead to less choice, less innovation and increased prices for customers.

“We’ve provisionally found that these three firms secretly shared out the market and colluded on prices for construction products used in many building projects across Great Britain.

“The CMA does not tolerate such practices and will use our enforcement tools to crack down on those it believes are taking part in illegal cartels.”

As part of a settlement process, Stanton Bonna and CPM have admitted to participating in the alleged cartel and have agreed to pay fines, which will be determined at the end of the CMA’s overall investigation. FPM is not part of this settlement and, at this stage, no assumption can be made that it has broken the law.