In the United Kingdom under the Merchant Shipping Act 1995, jetsam, flotsam, lagan and all other cargo and wreckage remain the property of their original owners. Anyone, including recreational divers and beachcombers, removing those goods must inform the Receiver of Wreck to avoid the accusation of theft. As the leisure activity of Wreck diving is common, there are laws to protect historic wrecks of archaeological importance and to protect war graves.
There has been a lot of discussion around the net about the status of cargo that washed ashore from the wreck of the Napoli offshore from Branscombe, England. This should answer those questions.