FullWings:
A circling manoeuvre is a visual segment of an instrument approach, not a 'visual approach'. The in-flight visibility, maximum distance from the airfield and operating altitudes are all exactly specified, as BOAC has pointed out. As are the actions to be taken if you lose your reference or reach any of the other limitations.
Gee, guys, I have probably as much flying time as any of you, plus I have worked with TERPs criteria and FAA instrument flight operations regulations and policy since 1970 and still do to this day as a professional.
In fact, my issue with BOAC on this subject is that my considered view, shared by lots of safety experts, that the circle-to-land maneuver is a very demanding maneuver, especially in minimal weather conditions and in a jet transport aircraft.
BOAC is of the opinion that it is just another routine aspect of instrument flying. I strongly disagree.
As to this particular accident, there is some reason that the captain, for lack of a better term, went on an excursion rather than flying a disciplined CTL pattern. Please note that I used the phrase "ad hoc visual" with reference to the captain's apparent actions. Please also note that I mentioned earlier in the thread the hazard of CTL in monsoonal rain conditions. Those hills were almost certainly experiencing upslope, moist conditions. (orographical lift)
The aviation community, both in the U.S. and Europe, is working to advance the use of 3-D approaches to virtually every runway end using RNP AR or at least Advanced RNAV (known as "APCH" in ICAO-speak). And, in RNP AR criteria CTL is specifically prohibited because of the high risk of the operation.