The Regulation of Investigatory Powers (Conditions for the Lawful Interception of Persons outside the United Kingdom) Regulations 2004
Part 1 of the Regulation of Investigatory Powers Act 2000 contains provisions about the interception of communications. Section 4(1) provides that the interception of a communication is authorised (and therefore lawful) if it is carried out for the purpose of obtaining information about the communications of a person who is, or is reasonably believed to be, in a country or territory outside the United Kingdom, it relates to the use of a public telecommunications service provided to persons in that country or territory and the person who provides that service is required by the law of that country or territory to carry out, secure or facilitate the interception in question.