They carry on when the light is red?
I have seen plenty take off early and do it myself to avoid having the traffic pile up behind me, but going through a light that has just turned red would seem to invite catastrophe.
I'm neither a driver nor a cyclist - just a pedestrian - but my impression is that, at least in my part of London, cyclists carry on through red lights much more frequently than cars.
Same. Depending on the intersection and traffic there are places in zone 1 where the traffic signals seem to be considered completely optional for cyclists. I have also found myself needing to use a death stare to get some cyclists to stop at a zebra crossing as well; this happens far more frequently with cyclists than I ever needed to for cars or HGVs.
Obviously, purely anecdotal.