The Co-operative Group, Sainsbury's, Waitrose, M&S and Morrisons have been praised for their fish-sourcing policies by the Marine Conservation Society.

The five supermarkets all achieved an MCS sustainability score of at least 68%. Asda fared worst, with 55%, although no discounters responded to the survey.

The Co-op was praised for eliminating all stocks from the MCS Fish to Avoid list while having the largest percentage of sales from the Fish to Eat list, which includes species such as coley, gurnard and dab.

All eight retailers that responded to the survey had improved their sourcing policies, MCS said. Further progress could come through delisting all of the Fish to Avoid list and improving labelling, it added.

"MCS wants all Britain's major supermarkets to use a sustainable seafood policy and give customers good information on sustainable choices," said MCS fisheries officer Sam Wilding.