So that just leaves me to ask you, Which part of MINIMUM DESCENT ALTITUDE don't you understand?
In your scenario you are below MINIMUM DESCENT ALTITUDE and climbing prior to (not having yet satisfied the minimum requirements) commencing a circling approach.
1.7.1 A circling approach is a visual flight manoeuvre.
Whilst in a "gentle climb to circling altitude", you are just waffling around IFR below MSA.
1.7.3 During visual circling or during a NPA, descent below the MDA
may only occur when the pilot:
a. maintains the aircraft within the circling area; and
b. maintains a visibility, along the intended flight path, not less than the minimum specified on the chart for the procedure; and
c. maintains visual contact with the landing runway environment (ie, the runway threshold or approach lighting or other markings identifiable with the runway);
and either
d. by night or day, while complying with a., b. and c. (at an altitude not less than the MDA),
But by strict letter of the law (and I've spoken to Casa on more than 1 occasion about this exact issue), its legal to do what I've described.
Yes it is legal but that climg to circling MDA is (Night) VFR, which we cannot avail ourselves of in airline ops.
As you know Airline RPT ops must be operated under the IFR!