Well, my main point was "which bit of London?". Driving in Hammersmith, Kensington etc. (basically the West End) is fine. People are courteous, and are generally driving expensive cars that they don't want to smash up. City driving is very different from town driving and country driving. You have to be assertive. In my London you have to make sure that people know you want to change lane, but they let you in with no hassle. If you just sit there with your right blinker on, waiting for someone to flash, of COURSE you are going to find it difficult
City driving can seem overwhelming to the uninitiated, but city drivers are generally far more skilled at it than day-trippers. There are parts of London that are a nightmare (North London can be pretty bad in my experience), but it's not London in general.
And the people in London are fine. It is tourists who make the place difficult to get around. In any bustling city, the locals are trying to get from point A to point B with the minimum of hassle. If you have a group of 10 people with cameras just suddenly stop in the middle of a busy street then of course they will feel unwelcome! They have just blocked a load of people from getting where they are going! OK, so tourists have a right to see the sights and amble around at a leisurely pace, but they should also be considerate as to where they choose to stop, or how they choose to arrange themselves (i.e. not 10-people wide on an 11-person-wide pavement!).
I have actually found the worst driving to be in Bradford. I had some guy get out of his car and storm towards me because HE hadn't stopped at a RED LIGHT and almost T-boned my car!
Everywhere has its own style of driving. I live in a town where people are inconsiderate, turn right from left-turn only lanes, and seldom indicate. Yet somehow I seldom see collisions, and anything more than a fender-bender is very rare. When I go to my parents' town I now get frustrated at the old farts who mince about at half the speed limit. Now I know that's their perogative, but they get so uptight when you eventually overtake, often accelerating in an attempt to stop you getting past!
London is no less friendly than anywhere else, apart from perhaps small villages where everyone greets everyone. But I can appreciate it is a little intimidating for those not used to a very big city.