UK supermarkets are under renewed scrutiny over their tuna sourcing practices following the EU’s decision to block measures designed to protect vulnerable Indian Ocean tuna stocks.

In a move marking a major legal win for environmental campaigners, the European General Court has sided with NGOs Blue Marine Foundation and Bloom Association, ruling that the European Commission must review its decision to oppose a 72-day ban on the use of drifting fish aggregating devices (FADs).

FADs are a fishing method heavily criticised for their damaging impact on tuna populations and marine ecosystems.

The ruling sets a legal precedent, increasing transparency and access to justice for campaign groups challenging EU decisions that undermine environmental law.

The ruling means Blue Marine is now urging UK supermarkets to stop selling tuna caught using drifting FADs, warning that despite public sustainability commitments, most major grocers continue to stock brand-name tuna linked to the practice.

Blue Marine head of investigations Jess Rattle: “UK consumers are being misled by supermarket sustainability claims. Retailers know the harm these devices cause, but many still sell tuna caught with them.”

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The decision follows in the wake of the 2023 investigation by Blue Marine, which found that while several supermarkets have banned drifting FADs from their own-label tuna, many still stock brands such as John West and Princes, which source from fleets using the technique.

The NGO said Marks & Spencer is the only UK supermarket to fully exclude tuna caught using drifting FADs across all its products.

“It’s another reason why our customers can trust that M&S is doing the right thing,” said M&S Food head of agriculture and fisheries Steve McLean.

The court ruling and fresh calls from Blue Marine are expected to intensify pressure on retailers ahead of sourcing reviews, with campaigners now wanting retailers to stop signing any new supply agreements for tuna caught with drifting FADs.

Meanwhile, new polling by Blue Marine shows 59% of UK shoppers would avoid buying fish if they knew it was caught unsustainably.

However, 17% say they don’t trust current seafood labelling, highlighting confusion and a lack of transparency in the aisle.

Blue Marine CEO Clare Brook added: “This is a big win in the battle to stop destructive overfishing. But until supermarkets take proper action, UK consumers are still unknowingly supporting harmful practices.”