Lead author Catherine Hobbs said: 'It's nearly impossible for consumers to know what they are buying.
The called for more stringent food labelling so people know what species they are eating.
The researchers tested 117 tissue samples from 90 different retailers in the United Kingdom: 78 from fish and chip shops, which were battered and fried when collected, and 39 from fishmongers, which were either fresh or frozen.
Shark and chips? Investigation finds endangered sharks routinely sold in high street fish and chip shops
"People might think they are getting a sustainably sourced product when they are actually buying a threatened species", Hobbs said.
University of Exeter scientists exposed a trade in endangered sharks by fishmongers, fish and chip shops, Chinese restaurants and supermarkets.
Although the European Union prohibited the fishing of spiny dogfish (or Squalus acanthias) in its waters in 2011, fisheries in the United States and Canada in particular continue to export catches to the UK.
"There are also health issues", noted Hobbs.More news: United Kingdom trade minister says European Union 'irresponsible' to refuse to reopen Brexit deal
Ninety per cent of shark products - typically sold as huss, rock salmon or rock eel - were found in tests at takeaways to be the globally threatened spiny dogfish. "Knowing what species you are buying could be important in terms of allergies, toxins, mercury content and the growing concern over microplastics in the marine food chain".
This makes it much harder for buyers to know the origin - and the species - of the fish, suggesting the chip shops are unaware of the scale of endangered fish they appear to be selling, researchers said.
Endangered species of hammerhead and dogfish are among the sharks being sold as food in the United Kingdom, researchers have revealed.
For the first time in Europe, shark fins from a nationwide Asian food wholesaler destined for restaurants and supermarkets were also analysed using mini bar codes.More news: Miami vs. Virginia Basketball Highlights (2018-19)
The researchers also tested 30 shark fins seized by the UK Border Force on their way from Mozambique to Asia which derived from the endangered bull shark.
Researchers at the University of Exeter also found fins of shark species unknowingly sold by a British wholesaler included scalloped hammerheads, which are endangered globally, as well as shortfin mako and smalleye hammerhead sharks.
The shocking find was made using "DNA barcoding', a method that uses a designated portion of a specific gene to identify an organism to species".
Fin samples included scalloped hammerheads, which are endangered globally and subject to global tread restrictions, according to the researchers.More news: Tesla begins sales of cheaper Model 3 car variant in China
Senior author Andrew Griffiths, a lecturer in biological science at the University of Exeter, told CNN that sharks are particularly at risk of population decline thanks to their slow rate of reproduction.