The Spanish government is to take legal action in the US courts to force an exploration company to reveal whether 17 tons of gold and silver coins, worth an estimated £250 million, were recovered from a wreck off the British coast.

Florida-based Odyssey Marine Exploration has refused to say where the treasure was found, but it is widely believed to have come from the British sailing ship Merchant Royal, which sank off the Isles of Scilly in 1641 carrying Spanish cargo.

Covington and Burling, a law firm that has offices in London and Washington, has been instructed by Spain to require disclosure as the first step in a legal action that could lead to the bounty being declared Spanish property.