John West has been accused of breaking a promise to consumers by continuing to use "destructive" fishing methods to catch tuna.
The latest league table for tuna sold by supermarkets and companies produced by Greenpeace ranks the firm last because 98% of its tuna is caught using "fish aggregation devices" which kill other marine wildlife including sharks and endangered turtles.
John West is using the fish aggregation devices in its fishing fleet despite a promise in 2011 that 100% of its tuna would be sustainable by 2016.
The rankings put Waitrose, Marks & Spencer and Sainsbury's in the top three spots, while Tesco made great progress to jump up the table to fourth place, Greenpeace said.
In response to the rankings John West insisted it was "fully committed" to the protection of the marine environment and sustainable sourcing and it remained committed to its 2011 pledge.
It said it defined sustainably sourced fish as not being endangered or threatened, caught by well-managed fisheries with scientifically based quotas, via responsible fishing methods and traceable from catch to consumer.
"We believe our commitments are best achieved by employing a number of practices and innovations all of which will work together to minimise bycatch, protect stock levels, preserve oceans, improve working conditions and ensure safe and legal practices throughout every aspect of our operations," the company said in a statement.
But Ariana Densham, oceans campaigner at Greenpeace UK, accused the company of only catching a "pathetic" 2% of its tuna in a way that minimises harm to other marine life.
"It's a great achievement that all major supermarkets in the UK now only use fully sustainable tuna in their own brand products, caught using the pole and line method or in nets without fish aggregation devices, which minimises harm to other animals.
"But John West continues to plumb the depths of irresponsibility - flooding our shelves with cheap tuna which comes at a huge cost: the indiscriminate killing of marine life. It's also undermining the world-leading standard set by UK supermarkets.
"The tide is turning on companies which sell unsustainable tuna and unless John West keeps its promise to UK consumers to stop using destructive fishing methods, it will find itself cast adrift."
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