Morrisons and Marks & Spencer broke land use laws to stop rival supermarkets opening nearby stores, according to the competition watchdog.

The Competition and Markets Authority (CMA) said it has taken action against the retailers to address 65 unlawful agreements which restricted local competition.

This included 55 breaches by Morrisons and 10 breaches by M&S.

Morrisons told the regulator it is working to rectify the breaches swiftly.

M&S said it was “disappointed” by the breaches and argued the agreements “did not adversely affect competition”.

The CMA’s probe related to the Groceries Market Investigation (Controlled Land) Order (CLO), which was brought in in 2010 to stop supermarkets imposing restrictions that block rivals from opening competing stores nearby.

The watchdog has already found similar breaches by Tesco, Sainsbury’s, Asda and Waitrose.

The CMA said restrictions have already ended in 14 cases for Morrisons and five cases for M&S, but called on the chains to resolve the outstanding deal.

Adam Land, senior director of remedies business and financial analysis at the CMA, said: “At a time when the weekly shop is a source of financial pressure for many families, it’s crucial that competition between supermarkets is working well to help people get the best deals they can.

“These restrictive agreements by our leading retailers are unlawful.

“There can be no excuses made for non-compliance with an order made in 2010, especially when we know the positive impact for shoppers of new stores on the high street.”

A Morrisons spokesman said: “We co-operated fully with the investigation and accept its findings.

“We now plan to rectify the outstanding breaches quickly.”

An M&S spokesman said: “We are disappointed that having worked closely with the CMA over the past three years, it has highlighted 10 breaches, five of which are historic and expired.

“These have made no practical difference to the activity of our competitors or our tenants and did not adversely affect competition.

“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.”