38.This section deals with authorisations for intrusive surveillance. Such authorisations may only be granted by chief constables in the police forces.
39.By virtue of subsection (2), intrusive surveillance authorisations cannot be granted unless specific criteria are satisfied, namely that the chief constable is satisfied that:
	the authorisation is necessary for the purpose of preventing or detecting serious crime (which is defined in section 31(6)); and
	the authorised activity is proportionate to what is sought to be achieved by it.
40.An additional factor which must be taken into account is specified in subsection (3). The chief constable must be satisfied that the information which it is thought necessary to obtain by the authorised conduct could not reasonably be obtained by other means.
Commentary on Sections Authorisation of surveillance and human intelligence sources Section 10:  Authorisation of intrusive surveillance