The majority of UK restaurant chains use unsustainable fish or fail to give transparent information to diners about the origins of their seafood according to findings from the Marine Conservation Society (MCS).

It found more than half of the restaurants assessed served seafood from overfished supplies with sea bass, whitebait, cod and king prawns all regularly featuring on menus despite coming from fisheries the MSC advises to avoid because the origin of the fish is unclear.

After assessing large restaurant chains, MSC with Fish2Fork found YO! Sushi and Pret to have the most sustainable approach to supply chains and were responsible when buying seafood.

Yo! was given a blue fish rating of 4 out of 5 and Pret gained a 4.5 rating.

MSC rates restaurants with either red or blue fish out of a maximum of five – five blue fish is the highest rating while five red is the lowest score possible.

Other brands identified for good practice were Table Table – the Whitbread restaurant group, Hungry Horse and Zizzi which were all found to exceed the minimum expectations.

At the other end of the scale, Bella Italia, ASK, Harvester, Wagamama, Café Rouge, Chiquito, and Frankie & Benny’s were given Fish2fork red fish ratings. The lowest was Bella Italia with 1.5 red fish. The lowest possible rating is 5 red fish.

MSC said: “While it is disappointing that any chain restaurants have merited a red fish award, there were indications that none of the seven that were given red fish ratings would need to introduce enormous changes to earn a blue fish award.”

The biggest issue identified by the Fish2fork and MCS project was lack of transparency on the sources of the seafood being served. Of the restaurants assessed, eight out of 12 served at least one species of seafood that could have come from an overfished fishery.

Only half of the restaurant chains were willing to provide full answers to questions by Fish2fork about the sources of their seafood, which MSC said makes it difficult for the public to be understand what they are eating and whether it comes from sustainably managed fisheries.

Tim Glover, co-founder and managing director of Fish2fork, said: “Some restaurant chains are making every effort to ensure the seafood they put on their menus is caught sustainably or farmed responsibly.

“But we believe the sector as a whole should be putting much more effort into sourcing practices and the information given to customers. Diners want to eat with a clear conscience, to know that their menu choices are not further damaging our hard-pressed seas.

“To do so, they need clear assurances from restaurants that the fish and shellfish offered to them come from a well-managed fishery or farm. Our assessments show that too many restaurants are either serving seafood we believe should be kept off the menu, or are giving so little information on menus and websites that customers can have little clue to the origins.”