20. (1) The Minister may give an authorisation where, and only where, he or she—

(a) has received an application under section 21, and

(b) is satisfied that the conditions referred to in subsection (2) have been met.

(2) The conditions referred to in subsection (1)(b) are:

(a) that there are reasonable grounds for believing that a serious threat exists;

(b) that there is a reasonable prospect that the cessation of a mobile communications service within a geographical area would be of material assistance in averting that threat;

(c) that having regard to all the circumstances, including the importance of maintaining the availability of the mobile communications service in the geographical area concerned and the effect of a cessation on users, the giving of an authorisation is necessary and proportionate to its objectives.