Endangered sharks are routinely being sold to unwitting customers at fish and chip shops, an investigation has found.

Scientists tested fish passed off under umbrella names such as “huss”, “rock salmon” and “rock eel”, finding a majority came from sharks which are protected because of declining numbers.

The investigation also tested fin samples at fishmongers and fish wholesalers, finding evidence of imported hammerheads, which are subject to international trade restrictions because of their endangered status.

The team at Exeter University, who used DNA “barcoding” techniques to establish the provenance of samples, said their results show it is “impossible” for consumers to know what they are buying.

They called for more stringent food labeling so people know what species they are eating.

The shark most commonly found to be sold in the fish and chip shops investigated was spiny dogfish, a species that is illegal to catch intentionally in European waters.

The shark has been overfished for years thanks to its popularity, particularly in northern Europe, but is still favoured by takeaway shop owners because of its moist flesh and strong taste, the investigation found.

Dr Andrew Griffiths, who led the research, said vendors were deliberately confusing customers and regulators by labeling the product with ambiguous names that do not include the word “shark”.