Salvagers claim to have found the world's richest wreck – a British ship sunk by a Nazi submarine while laden with a £2.6 billion cargo that included gold, platinum and diamonds.

In a project shrouded in secrecy, work is due to start on recovering the cargo, which was being transported to the United States to help pay for the Allied effort in the Second World War.

The scale of the treasure trove is likely to unleash a series of competing claims from interested parties. Salvage laws are notoriously complex and experts say there could be many years of legal wrangling ahead.

In order to protect its find until the cargo is brought to the surface, the company that located the wreck has not released the name of the vessel or its exact location, but has given the ship the code name "Blue Baron".

It says the merchant ship, which had a predominantly British crew, had left a European port, laden with goods for the US Treasury under the Lend-Lease scheme, whereby the American government gave material support to the Allied war effort in exchange for payments.