An authorisation granted to a member of a public authority permits
that person to engage in conduct relating to the acquisition and
disclosure of communications data under Part I Chapter II of RIPA.
A notice given to a postal or telecommunications operator requires it
to disclose the relevant communications data held by it to a public
authority, or to obtain and disclose the data, when it is reasonably
practicable for them to do so. Both authorisations and notices are
explained in more detail within this chapter.