I understand the frustration people feel behind things moving slower than they ideally would like to go but if everyone chilled out a little and realised that tooting horns, accelerating like demons to be the first car at the narrow bit of the road, not speeding up at ambers, not letting any other cars out at junctions doesn't actually speed up your journey. You'll just spend slightly longer at the traffic queue at the next junction and in the grand scheme of things in London where most journeys are under 5 miles, you're talking minutes added to your journey.

Without enforcement, I can't see the 20mph being followed much. For most drivers, it feels too slow so it will creep up. The only thing I can see encouraging it, is for traffic lights to be rephased so that they work best (i.e. least waiting) for vehicles at 20mph (i.e. those at 30mph get stuck at every red for longer, those at 20mph get the golden run)