Personally I read the AIP stating a missed approach must be executed if entering cloud during a circling approach.
AIP ENR 1.5
1.10.1
e) visual reference is lost while circling to land from and instrument approach.
Note 1: For the purpose of this paragraph "visual reference" means the runway threshold, or approach lights or other markings identifiable with the landing runway clearly visible to the pilot and;
a) for circling approaches, clear of cloud, in sight of the ground or water and with a flight visibility not less than the minimum specified for circling.
I may be wrong with my interpretation of the rules... I wil stand corrected if so.
defiant.