The competition watchdog has slapped three building firms with more than £36 million in fines for taking part in an illegal price-fixing cartel.

FP McCann, Stanton Bonna Concrete and CPM Group broke competition law after working together to fix prices for almost seven years, the Competition and Markets Authority said.

The regulator said the firms, which supply concrete building products, worked together by allocating customers and illegally shared competitively sensitive information.

It said the firms kept prices artificially high as part of the arrangement, which “cheated” customers out of getting the best deal.

Between July 2006 and March 2013, senior executives from each of the firms took part in meetings to co-ordinate prices, a number of which were recorded by the watchdog.

Northern Irish firm FP McCann was hit with more than £25 million in fines for its part in the cartel, after not accepting its role in rigging prices.

Derbyshire-based Stanton Bonna and Somerset-based CPM were fined £7 million and £4 million respectively after their penalties were reduced for accepting responsibility.

All three firms produce concrete products such as drainage pipes, used in roads and water management projects.

At the time of the infringement, the firms were leaders in the sector and supplied major construction firms.

Andrea Coscelli, chief executive of the CMA, said: “These companies entered into illegal arrangements where they secretly shared out the market for important building products and agreed to keep prices artificially high.

“This is totally unacceptable as it cheats customers out of getting a good deal.

“The CMA will not hesitate to issue appropriately large fines in these cases and we will continue to crack down on cartels in the construction sector and in other industries.”

The announcement comes amid the CMA’s Stop The Cartels campaign, which aims to educate businesses about illegal trading practices.