I'm a little unsure about the law on box junctions. As I understand it
you can enter a box junction when turning right if the road you are
turning into is clear and when oncoming traffic stops you can proceed.

What happenes if this road then fills up as you are waiting (by
oncoming cars turning left)?

One other question, are u-turns automatically enforced, or is it
leanient (e.g. no fine for uturns on an empty road at 3AM)