Four of the UK’s biggest sports broadcast and production companies have been fined more than £4m for illegally colluding on freelance pay rates.

The UK’s competition regulator said the BBC, BT, IMG and ITV must pay a combined £4.24m after being found to have shared information about fees for freelance workers including camera operators and sound technicians.

Sky also admitted breaking the law but avoided a fine after alerting the the Competition and Markets Authority (CMA) to its involvement before the investigation began.

Freelancers are used by all five firms to create sports content and work on productions of live matches and events.

The CMA said it found 15 examples of two companies illegally sharing information about pay – such as day rates and increases – in order to co-ordinate how much to pay freelancers.

One of the companies told another they “want to be aligned and benchmark the rates” but had “no intention of getting into a bidding war”, the investigation said.

The regulator’s executive director for competition enforcement, Juliette Enser, noted how “millions watch sports on TV each day, with production teams working behind the scenes to make this possible” and that it was “only right they are paid fairly”.

“Companies should set rates independently of each other so pay is competitive – not doing so could leave workers out of pocket,” she said.

“Employers must ensure those who hire staff know the rules and stick to them to prevent this happening in the future.”

BT and IMG were each fined £1.7m, while the BBC must pay £424,000 and ITV received a £340,000 fine.

All four broadcasters told BBC News they co-operated fully with the investigation.

A BBC spokesman said it “takes its competition law obligations seriously and has co-operated with the CMA throughout its investigation”.

“The BBC was involved in three of the 15 infringements identified by the CMA and admitted liability for these as soon as possible,” he added.

“We highly value the freelancers we work with, both in Sport and across the BBC, and we will continue to work hard with the freelance community to invest in, and develop, talent.”

A BT Group spokeswoman said: “We take our competition law obligations seriously and co-operated with the CMA throughout this investigation.

“Having accepted the findings of this investigation, we have agreed to settle this case. We remain committed to making sure our obligations are embedded into all levels of our business and have taken a number of steps to strengthen our competition and compliance initiatives.”

An ITV statement said: “ITV is fully committed to complying with competition law and co-operated with the CMA throughout its investigation.

“In light of the CMA’s investigation we have implemented further enhanced competition law compliance measures across the business.”

IMG declined to comment.

On Friday, the CMA also launched a similar investigation into non-sports TV productions, with the BBC, ITV, Hartswood Films, Hat Trick Productions, Red Planet Pictures, Sister Pictures and Tiger Aspect Productions under the spotlight.