3Scope of warrants
(1)Subject to subsection (2) below, the interception required by a warrant shall be the interception of—
(a)such communications as are sent to or from one or more addresses specified in the warrant, being an address or addresses likely to be used for the transmission of communications to or from—
(i)one particular person specified or described in the warrant; or
(ii)one particular set of premises so specified or described; and
(b)such other communications (if any) as it is necessary to intercept in order to intercept communications falling within paragraph (a) above.
(2)Subsection (1) above shall not apply to a warrant if—
(a)the interception required by the warrant is the interception, in the course of their transmission by means of a public telecommunication system, of—
(i)such external communications as are described in the warrant; and
(ii)such other communications (if any) as it is necessary to intercept in order to intercept such external communications as are so described; and
(b)at the time when the warrant is issued, the Secretary of State issues a certificate certifying the descriptions of intercepted material the examination of which he considers necessary as mentioned in section 2(2) above.
(3)A certificate such as is mentioned in subsection (2) above shall not specify an address in the British Islands for the purpose of including communications sent to or from that address in the certified material unless—
(a)the Secretary of State considers mat the examination of communications sent to or from that address is necessary for the purpose of preventing or detecting acts of terrorism ; and
(b)communications sent to or from that address are included in the certified material only in so far as they are sent within such a period, not exceeding three months, as is specified in the certificate.
(4)A certificate such as is mentioned in subsection (2) above shall not be issued except under the hand of the Secretary of State.
(5)References in the following provisions of this Act to a certificate are references to a certificate such as is mentioned in subsection (2) above.