When riding in London a few years ago I came off my bike when a car driver - who hadn't seen me - turned across the road in front of me. I slammed on my brakes, and went over the handlebars only a few inches before hitting the car. I landed on the road with my hip and my head whiplashed over into the road. If I hadn't been wearing a helmet I would undoubtedly have fractured my skull, and possible worse. Since then I've been a vocal proponent of helmets - in London - because this accident was nothing to do with my riding. I had a front light on, a reflective vest and light-coloured clothing.
The real issue for me is cycling infrastructure. London is getting sort-of better. There are cycle "superhighways", but they're quite narrow and have their fair share of idiot cyclists who ride very fast and loose, and make it dangerous for other cyclists. If there was better infrastructure there might be a critical mass of more sedate cyclists who set the tone for cycling in general, so everyone takes account of that new paradigm. Until that happens, I don't think there's a good safe way of cycling in somewhere like London without a helmet.
The real issue for me is cycling infrastructure. London is getting sort-of better. There are cycle "superhighways", but they're quite narrow and have their fair share of idiot cyclists who ride very fast and loose, and make it dangerous for other cyclists. If there was better infrastructure there might be a critical mass of more sedate cyclists who set the tone for cycling in general, so everyone takes account of that new paradigm. Until that happens, I don't think there's a good safe way of cycling in somewhere like London without a helmet.