I thought ATS surveillance was simply RADAR identified (RADAR control - not necessarily RADAR vectors). If you're in RADAR controlled airspace, you have to maintain the last instruction (all of it) until within the circling area, or on the centreline.
Obviously, it would be a lot easier if controllers were more in the habit of saying (at appropriate airports) "descend to [2000],
track as required for final, cleared visual approach" !!
