below is the full text of vectoring for visual approach from Doc4444.
8.9.5.1 The radar controller may initiate radar vectoring of an aircraft for visual approach provided the reported ceiling is above the minimum altitude applicable to radar vectoring and meteorological conditions are such that, with reasonable assurance, a visual approach and landing can be completed.
8.9.5.2 Clearance for visual approach shall be issued only after the pilot has reported the aerodrome or the preceding aircraft in sight, at which time radar vectoring would normally be terminated.