The main danger to cyclists for city riding is, however, not the cars (which are mostly stationary and generally fairly predictable and easy to avoid even when in motion), but the pedestrian in the roadway. This particularly applies in shopping streets and tourist areas, with London's Oxford Street - which is a major East-West route and heavily frequented by shoppers as well as tourists who are unused to traffic coming from their right - being about the worst in my experience. Pedestrians are unpredictable and frequently unwary, a lethal combination.
The primary danger that pedestrians - themselves fairly soft targets - present to a cyclist is that in the event of an impact, regardless of who is at fault, the cyclist usually bounces off them (since the impact is invariably glancing) into the nearest bus, pointy piece of street furniture or skip or else just cartwheels down the road picking up gravel rash. In order to minimise the overall damage to the parties involved, it is therefore best to react to an unavoidable and imminent impact by leaning fairly sharply into the target, thus (a) transferring more kinetic energy to the pedestrian, who will probably fall over but not actually bounce 20 yards like the cyclist would otherwise, and (b) increasing the chance that the effect of the impact will just be to put the cyclist back on an even keel allowing them to stop under control to pick up the pieces. It may occasionally be possible in some circumstances to use a rugby-style hand-off, but it is almost always more desirable to have both hands on the bars so as to retain control after the collision, so the best thing is to lead with your shoulder such that your arms - and hence front wheel - don't get wrenched to one side (as I mostly don't wear a plastic hat, I am not sure if they are likely to get in the way though)
Although this may seem callous, this technique kept me alive for a couple of years as a dispatch rider. I feel that it is probably justifiable on utilitarian grounds since not only are the likely physical injuries reduced, but it also lessens the likelihood of post-traumatic stress disorder to the pedestrian, bystanders and members of the emergency services in the event of the cyclist suffering a hideously messy death between the wheels of a passing artic.