Pedestrian guide to cross the road in London?

You cross when there is no traffic. In your example this would mean when the lights are red and there are no cars turning into the road; there is a brief period as the lights change when no cars at all are allowed, and pedestrians often take advantage of this.

You can, of course, cross at any time if there is no traffic at all; you may gather disapproving looks from those who are training children (or dogs) only to cross when the lights are in their favour.

And if you come from one of those countries where they drive on the right, you have to remember which way to look before you step out. Fortunately on many busy or confusing crossings (like this one) the authorities have painted 'LOOK RIGHT' just in front of the kerb.

This is the official guidance, from the UK Highway Code: http://www.highwaycodeuk.co.uk/rules-for-pedestrians---crossing-the-road-7-to-17.html and the following two pages.

Specifically, Rule 8: At a junction. When crossing the road, look out for traffic turning into the road, especially from behind you. If you have started crossing and traffic wants to turn into the road, you have priority and they should give way. They might hoot at you, but they won't deliberately run you over.

So if traffic waiting to turn is stopped at a red light when you start to cross, you have priority over them if the lights change while you are still crossing.

Most busy junctions with traffic lights (with or without pedestrian lights) will have central "islands" so you can cross each half of the road separately. In that case, each half-crossing is considered separately - when you reach the middle, stop and check the traffic situation (and/or the lights) again.

Note, only the Highway Code rules explicitly stating "must" or "must not" are legal requirements, but all of the rules are considered relevant when determining legal liability, in any situation.

In towns with complicated road junctions, one-way streets, etc, you will often find a sign painted on the road surface saying "pedestrians look left" as a warning that traffic is coming from the opposite direction from normal. (The UK drives on the left, so traffic usually approached you from the right).

Actually, vehicles with 4 or more wheels are not really the problem. The troublemakers are usually cyclists who have no insurance to lose if they have an accident, no registration marks that can be picked up on CCTV, and who consider that laws only apply to other people...