(1)Subject to the following provisions of this Act, the chief constable of every police force shall have power to grant authorisations for the carrying out of intrusive surveillance.
(2)No such authorisation shall be granted unless the chief constable granting it is satisfied—
(a)that the authorisation is necessary for the purpose of preventing or detecting serious crime; and
(b)that the authorised surveillance is proportionate to what is sought to be achieved by carrying it out.
(3)The matters to be taken into account in considering whether the requirements of subsection (2) above are satisfied in the case of any authorisation shall include whether the information which it is thought necessary to obtain by the authorised conduct could reasonably be obtained by other means.
(4)The conduct that is authorised by an authorisation for the carrying out of intrusive surveillance is any conduct that—
(a)consists in the carrying out of intrusive surveillance of any such description as is specified in the authorisation;
(b)is carried out in relation to the residential premises specified or described in the authorisation or in relation to the private vehicle so specified or described; and
(c)is carried out for the purposes of, or in connection with, the investigation or operation so specified or described.