Two merchant shipwrecks discovered off Chesil Beach and believed to date back to the 18th century have been granted protected status.

The wrecks, containing 15 cast iron cannons, have been given protection by the Department for Digital, Culture, Media and Sport on the advice of Historic England.

The rare cannon-site wreck lies in two parts at the eastern end of the beach near Portland and was discovered by divers of the Weymouth-based Shipwreck Project in 2010.

John Glen, minister for arts, heritage and tourism, said: "It's important that we protect these two sites that are part of our country's seafaring and naval history.

"The shipwreck off Chesil Beach is a rare discovery and by protecting it we can encourage further study of the site."

The eight cast iron cannons discovered on the inshore site were identified as English 24-32 pounders cast between 1650 and 1725.

The offshore site, believed to be the wreck of a wooden sailing ship, lies 220m south of this and consists of seven cast iron cannons dating back to the second half of the 17th century.

Historic England say it is possible the cannon sites could be the Dutch West Indiaman ‘De Hoop’, which stranded at Chesil Cove in 1749, and British cargo vessel ‘Squirrel’ which stranded on Chesil Beach in 1750.

A First World War mine-laying U-boat found off Whitby in North Yorkshire has also been granted protective status.

The wreck is a 1916 German Imperial Navy UC-70 mine-laying submarine which sank 40 ships during the war before being bombed in August 1918 with the loss of all its crew.

Chief executive of Historic England Duncan Wilson said: “These wrecks are separated by 280 miles and almost 300 years but they both comprise important elements of our maritime heritage.

“The importance of the UC-70 lies in its historical interest and the vulnerability of its component parts as well as its sensitivity as a war grave.

“The Chesil Beach wreck site is also important but for different reasons – it’s rare to discover wooden ships of this age surviving on the seabed with so many cannons.”

Historic England is also investigating the new discovery of a shipwreck at Tankerton, near Whitstable in North Kent, which could date back as far as 1200AD.