16Obtaining secondary data
(1)This section has effect for the purposes of this Part.
(2)In relation to a communication transmitted by means of a postal service, references to obtaining secondary data from the communication are references to obtaining such data in the course of the transmission of the communication (as to which, see section 4(7)).
(3)In relation to a communication transmitted by means of a telecommunication system, references to obtaining secondary data from the communication are references to obtaining such data—
(a)while the communication is being transmitted, or
(b)at any time when the communication is stored in or by the system (whether before or after its transmission).
(4)“Secondary data”—
(a)in relation to a communication transmitted by means of a postal service, means any data falling within subsection (5);
(b)in relation to a communication transmitted by means of a telecommunication system, means any data falling within subsection (5) or (6).
(5)The data falling within this subsection is systems data which is comprised in, included as part of, attached to or logically associated with the communication (whether by the sender or otherwise).
(6)The data falling within this subsection is identifying data which—
(a)is comprised in, included as part of, attached to or logically associated with the communication (whether by the sender or otherwise),
(b)is capable of being logically separated from the remainder of the communication, and
(c)if it were so separated, would not reveal anything of what might reasonably be considered to be the meaning (if any) of the communication, disregarding any meaning arising from the fact of the communication or from any data relating to the transmission of the communication.
(7)For the meaning of “systems data” and “identifying data”, see section 263.