Cut and pasted from the Manual of Air Traffic Services
10.3 Visual Approach
When an aircraft is cleared for a visual approach the clearance must include, where
necessary, a level restriction to ensure that:
a) the aircraft remains within radar cover; and
b) the pilot does not descend below the base of controlled airspace.
10.4 Final Approach
10.4.1 Aircraft on radar approaches should be positioned so as to maintain a period of level
flight before commencing descent on:
a) the nominal glide path for a surveillance radar approach; or
b) the glide path of a pilot interpreted approach aid;
except in an emergency or when continuous descent approach procedures are in
operation.
10.4.2 Aircraft should be vectored to close the intermediate and final approach tracks at not
less than 5 miles from touchdown.