Eventually a sergeant told me I needn't give my details, but I still had to be searched. Not wanting to be unreasonable, and having nothing to hide, I agreed. The officer who searched me scrutinised every scrap of paper in my wallet, passing items to his colleague, who copied down personal details. When I asked what sort of offensive weapon he expected to find there he replied, with a straight face, "razor blades". All the while our faces were being videoed by a police camera team.
The police said all this was "for your own protection". When I want police protection I'll ask for it.
We were not a gang of tattooed, knife-toting skinheads. We are short, bespectacled and rather feeble-looking specimens - a PhD student, a school teacher and a care worker.