Footage shows Danish journalists approaching and filming a suspected Russian “spy ship”.

“Ghost ships” are mapping offshore wind turbines, underwater data cables and other pieces of infrastructure in the North Sea – in preparation for a campaign of sabotage in the event of conflict with the West, according to an investigation.

Moscow is alleged to have deployed ships - including the Admiral Vladimirsky - to carry out underwater surveillance and map key sites for possible disruption to European communications and energy supplies – infrastructure that is sometimes shared with Britain – according to the report by public broadcasters in Denmark, Norway, Sweden and Finland.