Marks and Spencer Group PLC and Morrisons have said they will end their use of unlawful land agreements to stop rivals from setting up near their stores.
A review by competition watchdog the Competition and Markets Authority (CMA) identified 65 cases where the supermarkets had either set up unlawful agreements that stopped land being used by a rival supermarket or imposed restrictions on landlords.
Morrisons, which was described as having the poorest compliance record the CMA had seen, breached the rules 55 times between 2011 and 2020, and M&S in 10 cases.
Morrisons said it would address the 41 restrictions still outstanding while M&S said it would deal with the outstanding five agreements.
"These restrictive agreements by our leading retailers are unlawful. There can be no excuses made for non-compliance with an order made in 2010," Adam Land, senior director of remedies, business and financial analysis at the CMA, said.
An M&S spokesperson told Reuters its breaches made no practical difference to the activity of its competitors and did not adversely affect competition.
But the spokesperson added: "We are remedying these immediately, continuing to work with the CMA, and have introduced tighter internal governance and compulsory training to prevent it happening again.”
J Sainsbury PLC and Asda in June were reported by the CMA for similar breaches, while Tesco PLC and Waitrose were cited in 2020 and 2022 respectively.