Consumers should “completely avoid” buying UK-caught cod, the Marine Conservation Society (MCS) has said, as it warned that populations have reached a dangerous point of decline despite zero-catch recommendations.

The MCS, an environmental charity, publishes a Good Fish Guide to help consumers and businesses make sustainable seafood choices.

On Thursday it downgraded all UK-caught cod to the worst possible rating, recommending consumers choose European hake as a flaky white fish alternative.

Kerry Lyne, Good Fish Guide manager, called the downgrade a “warning signal”, and said the UK government needed to “address these concerns to allow stocks to recover”.

The ratings for trawled scampi have been downgraded for the same reason – now, only pot- or creel-caught scampi are recommended by the guide.

Cod populations have been in decline since 2015. The main cause is overfishing, although changing sea temperatures and other ecosystem pressures have affected breeding and juvenile survival.

Last year the International Council for the Exploration of the Sea (ICES) recommended a zero-catch policy for 2026 in the North Sea and adjacent waters.

It said that at this stage of decline, commercial fishing would risk pushing cod populations in the North Sea below the numbers needed for safe reproduction.

This advice has not been followed, but in December the minister for food security and rural affairs, Angela Eagle, announced a 44% cut in cod fishing for 2026. The decision was made in annual negotiations with the EU and Norway about their shared stocks.

At the time, an industry publication reported that fishers were “reluctantly resigned to the cut” as they were seeing fewer cod than usual.

Concerns about cod fishing echo those expressed over mackerel this time last year. When persistent overfishing caused by quota disagreements between the UK and its coastal neighbours depleted fish stocks, mackerel was removed from the Good Fish Guide recommended list.

More recently, Waitrose announced that it will stop selling mackerel by 29 April, saying fishing must be kept within “sustainable limits”.

Last year, the government’s allowed-catch level for mackerel was set 32% above the ICES advice.

Chris Graham, head of sustainable seafood at the MCS, said: “It’s deeply concerning seeing so many of our iconic fisheries – from cod to mackerel – under increasing pressure.”

He echoed Lyne’s calls for the government to take strong action in transitioning to low-impact fishing practices to “help rebuild stocks and reduce reliance on imports”. About 80% of the seafood consumed in the UK is imported.

The MCS has asked consumers to consider more sustainable alternatives to UK cod, such as Icelandic cod, which is abundant and not subject to overfishing. More locally, European hake is recommended as a sustainable choice, as is haddock, particularly if caught in the North Sea or west of Scotland.

Other options for shoppers wanting to make sustainable choices include seabass or plaice from the North Sea, and UK-farmed seafood such as blue mussels and freshwater trout.

The MCS updates its Good Fish Guide advice twice a year, depending on the latest scientific advice. In particular it looks at stock levels and plans for management.