The UK supermarket sector has much work to do to improve its overall ethical and environmental performance, Ethical Consumer’s latest product guide to supermarkets has claimed.

The Co-op and Marks & Spencer were declared the UK’s most ethical supermarkets even though both scored relatively poorly on the magazine’s ethical scoring system.

Although Waitrose was at the top of the scoreboard with a rating of six out of 20, compared with the Co-op and M&S which both scored an overall 5.5, Ethical Consumer made a qualitative judgment to declare the Co-op and M&S the leaders.

This was because Waitrose only received a middle rating for the management of workers’ rights in its supply chain where M&S and the Co-op were rated best, a spokesman said. Waitrose, however, was recommended as the best online retailer.

Asda, Sainsbury’s and Tesco were the poorest supermarket performers.

The conclusions were reached by rating 11 of the UK’s leading supermarkets for almost 20 different ethical and environmental criteria, including the use of controversial palm oil to policies on tackling climate change.

The product guide also saw Aldi and Lidl fall under the spotlight for the first time. It said the surprising finding was that the ethical performance of the German discounters was not as bad as many were expecting. A shop survey of Aldi and Lidl revealed that a good range of Fairtrade items were available. However, only a limited range of organic vegetables were on display and neither supermarket sold organic meat.

Heather Webb, the author of Ethical Consumer’s product guide to supermarkets, said: “Supermarkets need far more robust policies on a vast swathe of ethical issues including treating their suppliers fairly to their continued support of inhumane factory farming. UK supermarkets still have such a long way to go ethically that in most cases your local independent grocery store or wholefood shop will be the most ethical place to shop.”

However, she said that given the scale of discounts that both Aldi and Lidl offered and their pared-down business model, Ethical Consumer had expected ethical policies to be thin on the ground.

“While they won’t win any prizes, we were genuinely surprised by the level of ethical engagement that both Aldi and Lidl displayed,” Webb said.