Re: @ElReg!comments!Pierre = @Hugh Pumphrey - Track Stand? Bah.
It's not illegal for a car to stop in an advanced stop box, it's treated as two stop lines. If the light changes and you haven't cleared the box, you have to wait in the box for the light go green. The small cycle lane on the left which penetrates the first line is what allows cyclists to advance to the second line in the box without having to stop at the first line.
It's perfectly legal for a car to cross the first line under a green light, then stop before exiting the box should the light turn against them.