Leading supermarket chain Tesco has received criticism from environmental campaign group Greenpeace after it was revealed that the store stocks tuna that is not classed as sustainable.
Fellow supermarket Asda also sells unsustainable tins of tuna, but has vowed to cease doing so by the end of the year.
However, Tesco said in 2012 that it would switch its own-brand cans of fish for tuna that was caught in a more environmentally friendly way - a promise that it has failed to keep.
This was part of the supermarket's bid to improve its image following last year's horsemeat scandal.
Ariana Densham, oceans campaigner for Greenpeace, said: "This is pure hypocrisy from Tesco. The supermarket that promised to be totally upfront about where the food they sell us comes from is now rolling back their pledge to protect the oceans."
Chef Hugh Fearnley-Whittingstall is backing Greenpeace's campaign and has been outlining the concerns surrounding unsustainable fishing in his 'Fish Fight' television programme.
The controversy stems from the purse seine method, which uses fish aggregation devices to attract the fish before scooping them up in large nets. This often leads to turtles, sharks and stingrays being caught too, which can result in their unnecessary death.
Oriental and Pacific - a tuna brand sold by Tesco - is sourced in this way, while fish found in sandwiches and ready meals has also been found to be unsustainable.
Greenpeace wants Tesco to ensure all the tuna it stocks has been caught using the more sustainable pole and line method.
The organisation has published a 'Tuna League Table' to support its campaign, which reveals that Morrisons, the Co-operative, Waitrose, Sainsbury's and Marks and Spencer all take measures to ensure that their own-brand tuna is sourced in an environmentally friendly manner.
Other popular brands of tuna such as John West and Princes also use the purse seine fishing method, but have recently reduced how often they do so to make their products slightly more environmentally friendly.