The Royal Mint is to make silver coins from bullion cargo recovered from a British ship sunk more than 70 years ago by a German U-boat.

A limited number of 20,000 coins will be struck, costing £30 each, available from April 21, and are likely to appeal to collectors and anyone interested in maritime history.

The Royal Mint said it was the first time coins have been created from the shipment of silver bullion which was being carried on the SS Gairsoppa, which was sunk off the coast of Ireland on February 17, 1941.

The vessel was bringing supplies to Britain from India, including tea and pig iron, but broke free from a protection convoy during a heavy storm and was spotted and attacked by a German U-boat.

The ship spent 70 years under the sea before being located in 2011, 300 miles off the Irish coast, at a depth of three miles - half a mile deeper than the Titanic.

A US company recovered silver, some of which was passed to the Royal Mint for striking the coins, which are edged with the name SS Gairsoppa.

Shane Bissett, the Royal Mint's director of bullion and commemorative coin, said: "This incredible story marks yet another exciting moment in the Royal Mint's fascinating 1,000-year history.

"The traditional Britannia coin design, Philip Nathan's elegant portrayal of a windswept Britannia looking out to sea, is the perfect image for the coins struck from SS Gairsoppa's long-lost cargo. We are so pleased to be able to bring these coins to the market at long last, albeit more than 70 years later than expected."