THIS is the eye-opening moment a 12ft long shark was spotted swimming just 10ft off a west Dorset beach.

Beachgoers were left stunned when the dorsal fin of the whopping fish broke the surface of the water at West Bexington. 

A small crowd gathered to watch as the shark swam up and down the shingle shoreline for more than a minute.

But the enormous fish turned out to be a young - and harmless - basking shark thought to have to come close in to the shore to feed on plankton.

The rare sighting of the basking shark, Britain's biggest fish, was caught on camera by Dickon Smith, a diving instructor from Bournemouth.

Mr Smith had only just returned from seven years in Egypt running shark diving tours when he spotted the shark while fishing for mackerel.

He now plans to report the sighting to the Shark Trust, the UK's only shark conservation charity.

The 43-year-old said: "I was down at the beach at West Bexington to do a spot of mackerel fishing, and had only been there a matter of minutes when I spotted a dorsal fin break the water.

"I spent the last seven years running shark diving tours in Egypt so I knew straight away it was a young basking shark. It was about 12ft long and was no more than 10ft from the beach.

"They are common off the south coast but it is unusual to see one so close in to the shore. Juveniles tend to be bolder than adults and this one had probably followed a plankton bloom.

"There were a dozen or so people on the beach and some people were following the shark as it swam up and down. There was huge excitement but most were fishermen so they knew it was a basking shark too.

"After about a minute it swam off.

"I have only just moved back home, so to see a shark this close was the last thing I was expecting. It's a wonderful reminder of the wildlife living just off our shores."

Basking sharks - Cetorhinus maximus in Latin - used to be fished for their meat, fins and liver oil until the species became protected in 1998.

They are Britain's biggest fish, capable of growing as long as 40ft, and the second biggest fish in the world after the whale shark.

They are one of only three shark species to feed on plankton.