Potentially there is a gap in the Highway Code between the requirement to stay out of a box junction unless your exit is clear (unless turning right) and the requirement to give way to pedestrians. However, the rule for box junctions is a law stating 'you must not' whereas the rule for giving way to pedestrians is guidance prefaced by the term 'you should', which suggests the former is potentially open to prosecution whereas the latter is less likely. Ultimately it is a matter of using your judgement in the situation - you could enter the box junction with your exit appearing to be clear only for a pedestrian to start crossing, and it would seem unreasonable to be punished for avoiding a collision.