Nick Reynolds wrote a 'How to ride in London' article which you can find here
> Yeah, there were a lot of posts about the MAGna Carta run seeming > dangerous, and people being glad to get back in one piece. All the > London riders I've spoken to couldn't believe those posts - it > seemed so much safer than normal London traffic. The benefit of > experience? Or mental adjustment to risk by London riders? > (probably both).Many years ago I used often to ride between Edinburgh and London, both as a London resident, and then later as an Edinburgh resident, so I got very used to the differences. When arriving in London as a non-resident it would take me a day or two to "rev up" to the fast aggressive decisive style of London traffic. When arriving in Edinburgh, used to a London style of riding, I had to very deliberately slow myself down, since the London style seemd to Edinburgh drivers to be maniacal. It was also unnecessary, since the dominant fast decisiveness you need to employ in London to keep your space in the traffic just isn't needed in gentler places.
I haven't ridden in London now for a decade, but as a London pedestrian I note that the traffic has actually slowed down an awful lot due to congestion. Lots of places which used to offer opportunities for a fast bike to swoop through the flow of cars, are now so congested that most overtaking is done of stationery or almost stationery cars. A 500cc-ish bike used to be the fastest thing through central London. I suspect it's now a pedal bike, or a very narrow light motorcycle.
But Edinburgh rush-hours are now beginning to show traffic behaviour like that which London has always had all the time -- drivers driving on the edge of their reaction times, happy to risk injury to others for the sake of a few feet or a second. It's only dangerous if your riding style expects drivers to behave more politely and to leave bigger margins of time and space.
I would advise those not used to it to behave like a car, taking a car space in the lane, etc., while observing the traffic and learning how it behaves.