People swimming off the coast of Britain may be “at risk” from killer grey seals that have got a taste for blood, scientists have warned.

A study into the cause of some particularly brutal injuries caused to porpoises in the North Sea has found DNA evidence to suggest seals are to blame.

Often considered as a cute and cuddly attraction for tourists, the seals are actually Britain’s largest carnivorous mammal and use their claws and powerful jaws to tear chunks out of their prey.

There are reported to be almost 200,000 grey seals off the coast of the UK, and tours are even offered to give people the chance to swim among them.

Yet according to a paper published in the Proceedings of the Royal Society B journal, it could only be a matter of time before mutilated porpoises start washing up on Britain’s shores to show what the seals are capable of.

According to The Telegraph, the team of scientists analysed 721 porpoise bodies that washed up on the Dutch coast over a 10 year period and were fresh enough to find marks on. Around 25 per cent showed visible signs of grey seal attacks.

Lead researcher Mardik Leopold of the Institute for Marine Resources and Ecosystem Studies in The Netherlands said it was now clear that the seals are “one of the main cause of death in harbour porpoises”.

“Many of the mutilated porpoises were found on Dutch shores used frequently by human bathers and surfers and there would appear to be no reason why humans may not be at risk from grey seal attacks,” he wrote.

Study co-author Lineke Begeman, from Utrecht University, told Discovery News: “People go on excursions to swim or dive with grey seals, unaware that these animals can be quite dangerous for human-sized animals. Most people consider them quite cute.”