6.— (1) A judge may, on application in that behalf by the superior officer to whom an authorisation was issued, if satisfied by information on oath of that superior officer justifying the variation or renewal of the authorisation—

(a) vary the authorisation, or

(b) renew the authorisation, on the same or different conditions, for such further period, not exceeding 3 months, as the judge considers appropriate.

(2) An application for a renewal under this section shall be made before the authorisation concerned, or any previous renewal of that authorisation, as the case may be, has expired.

(3) Where an application for a renewal under this section has been made and the authorisation concerned would, but for this subsection, expire during the hearing of the application, it shall be deemed not to expire until the determination of the application.