Avoiding a ticket
Prevention is obviously better than cure. Contrary to the image of selfish drivers deliberately stopping in boxes, the vast majority end up stuck through a variety of circumstances. Often they don't see the box or where it ends until it's too late.
You are actually supposed to stop and wait until the car in front has completely cleared the box before entering it. Even if the road ahead is clear, the car in front could stop and make you stop in the box. Yes this sounds crazy and will increase congestion but thems the rules. So the first thing to do is to hold back before entering it, especially in slow moving traffic, and wait until there is a space on the exit side big enough to fit your vehicle.. This will likely mean you get stuck in the no mans land of the junction or on a crossing but that's the law I'm afraid.
If you do find yourself in a box with your exit blocked, the following actions could avoid a ticket:
1. Inching forward very slowly without actually stopping (eg these cases won at adjudicator).
2. Rocking your car back and forth (eg this case)
3. Turning left or right out of the box to escape it
4. Moving into an adjacent vacant lane if there is one (eg photo below).
5. Reversing out
6. If you are unable to turn out of the box or go into another lane (due to moving traffic), showing the CCTV that you are attempting to do so can avoid a ticket. This could include turning the car as much as you can (or at least the wheels) and indicating, as early as you can, then moving as soon as you can. (eg this case)