My understanding of CAP371 is this. You can operate your FDP as defined by sectors/start time and the FDP finishes at on chocks at airport C. The company can take any route back to A they like. As far as I can tell, they could position you to the other side of the world via LHR T5 and that would still be legal. Immoral, but legal.
763 jock is correct on this, the record I have heard of somebody positioning after a duty was 21 hours (Hajj) and that is 21 hours of positioning not including the flying duty done before the positioning sector started.
You duty limits are governed by the state that you are in not the one where your licence was issued otherwise different nationality flight crews would cause all sorts of problems when working together.