Meat from endangered sharks, according to the study, is on the British menu.
DNA tests show that shark products for restaurants include two species that are extinct.
Consumers may not be aware of what shark to eat – and whether it comes from a sustainable population, say British scientists.
The United Kingdom plays a steady role in "damaging trade in endangered shark species," they say.
One of the two endangered sharks identified – comb hunters – is subject to international restrictions.
Researchers at the University of Exeter say that, despite a small number of samples, they have demonstrated the sale of endangered sharks, which has highlighted the global nature of harmful trade in endangered species.
"The discovery of swampy hammers in shark fins, which were sold for sale in the UK, shows how great the sale of these endangered species is," said Dr. Andrew Griffiths BBC News.
The research, which was published in the journal Science News, examined both shark fins intended for restaurants, and shark steaks sold to fishermen and chip stores.
He found that Squalus acanthias, a small shark classified as threatening extinction worldwide – and one of the northeast Atlantic populations threatened – was the main shark sold in chips shops under the generic name of geese, rock, rock salmon, or the fallow.
The shark was probably imported from areas where stocks are sustainable and generic names are allowed – but scientists say it's hard for customers to tell exactly what kind of sharks they eat and where they come from.
"It's almost impossible for consumers to know what they are buying," said Catherine Hobbs also from the University of Exeter.
"People may think they are getting a product of sustainable origin when they actually buy endangered species."
The renowned hammer shark has been identified among 10 shark fins imported for restaurant business in the UK. Fins are often used to make soup, a festive meal in some Asian cuisines.
How do we know the sharks end up on the British board?
Once the shark has been processed, it is difficult to see which species it comes from. That's why scientists have done DNA tests to find out what's going on in the human food chain.
They have collected more than 100 samples from chips and supermarkets in southern England. They also looked at the dried fins of sharks imported into Great Britain.
The type of DNA analysis, known as DNA coding, gave a look at the shark species on sale.
The DNA fragment can be linked to an online database known as the bar-code of life for animal identification.
What did the study find?
Of the 78 samples that were sold in chips stores in 2016 and 2017, about 90% of barbed fish came from.
Landing this shark is generally not allowed under EU rules, although sales were probably derived from more sustainable populations elsewhere, then imported and frozen, scientists say.
Of the 39 fresh and frozen samples obtained from fishermen, about half of Mustelus asterias, a shark-type shark, were assigned. This shark is considered the least worrying about the risk of extinction.
Sphyrna lewini was found in three desiccated shark fins in the United Kingdom. They could have been imported and deposited before international restrictions come into force until 2014.
This shark, which is not found in the waters of the United Kingdom, is focused on fins and is on the decline.
Where does the seafood eat?
Shark meat is consumed around the world and has been part of human food for centuries.
Between 2000 and 2011, however, according to the United Nations Food and Agriculture Organization, global imports of sharks, skates, rays and other cartilage have increased.
International trade in 12 species is regulated due to concerns about the risk of extinction.
However, there is a debate among scientists who can – if any – shark be considered sustainable and harvested for nutrition.
"Sharks are naturally more susceptible to overfishing because they do not produce much eggs and last long before they reach maturity – so they can produce offspring," said Dr. Griffiths.
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