An ominous voice speaks over footage of deep water. "There is a creature alive today who has survived millions of years of evolution without change, without passion and without logic. It lives to kill: a mindless eating machine. It will attack and devour anything. It is as if God invented the devil and gave him... jaws!"

Next we see a young woman swimming in the sea. A moment later, as she gasps and struggles, something drags her under.

This is a trailer for the 1975 blockbuster movie Jaws. Based on a novel by Peter Benchley, it tells of an American seaside resort terrorised by a great white shark. Now some experts are predicting that great whites could be coming to British waters.

Britain already has a huge number of sharks: according to some estimates, 10 million small ones and 100,000 larger ones.¹ They represent 40 different species, including lesser-spotted catsharks, smoothhounds, velvet-belly lantern sharks, mako and porbeagle sharks.

Some, such as catsharks and thresher sharks, are seen only in summer, when they follow mackerel and other seasonally migrating fish. And some - around 26 species - are hardly ever seen, because they live up to 2,500m below the surface of the sea.²

Many are small and quite harmless. Even the basking shark, which is as big as a bus, is rarely a threat to humans, since it lives on tiny creatures such as planktonA general term for small organisms drifting in the sea or freshwater. Krill fall into the category, and are actually a kind of small shrimp.. Only three people are known to have died in a shark attack in British waters, and that was in 1937, when a basking shark overturned a fishing boat.

But great whites, which can grow to five metres in length, are a different matter. In the US they are a growing concern, with five attacks recorded off the Cape Cod peninsula in the last 12 years - one of them fatal.³ Many beaches now have signs that read "Great white sharks frequent these waters."

The worry for Britain is that it offers a very similar habitat, particularly around Devon and Cornwall. An organisation called Ocearch, which tracks shark movements, believes that great whites may now be heading for these shores. 

This is partly because Britain has a lot of seals - over 130,000 according to experts at Plymouth University. And seals form a major part of some sharks' diets.

Water temperature is another factor. Though sharks can travel through seas as cold as 2.7C and as warm as 27C, 16C suits them best - and that is the meanThe mathematical average of two or more numbers. temperature of British waters in summer and autumn. With global warming this is rising, and could become the mean for winter too.

There have actually been reported sightings of great whites off Britain since 1965. But a team which investigated them found that out of 100 of these, only 12 were credible - and some of those could have been the same shark spotted more than once. 

Experts say that sharks should be more afraid of us than we are of them. More than 100 million are killed around the world each year,⁴ and the population is falling as a result of overfishing, climate change and plastic pollution. 

Should we welcome them?

Yes: Sharks are extraordinary creatures which very rarely attack humans. To see them in the water is a thrilling experience, and the arrival of great whites would add to Britain's biodiversity.

No: Even one person killed by a shark is one too many. If they become a common feature of British waters, people will be afraid to swim in the sea and the economies of coastal resorts will suffer.   

Or... We need to rethink how we see the sea. Great whites have more of a right to be there than we do, since it is their full-time habitat, but we have killed many more sharks than sharks have killed humans.

Plankton - A general term for small organisms drifting in the sea or freshwater. Krill fall into the category, and are actually a kind of small shrimp.

Mean - The mathematical average of two or more numbers.