That is pretty much what I said to him at the time (based on no legal knowledge/training) and he backed down eventually, even on the demanding that any photos be deleted (he was concerned I might have been taking photos of a jewellers display - I hadn't, which he could see when I showed him the images on the camera screen. Being polite and reasonable appeared to deal with this particular instance.

I have also previously had a run in with a ticket inspector on a train who took offence at my photographing a sunset. In that instance he argued that it was illegal to take photographs on railway property and again tried to confiscate my camera, probably committing an assault as he tried to grab it from me. In that case a number of people in the carriage turned on him and made it clear that he was behaving unreasonably and he backed down, not particularly graciously. Again I have no idea if he had any legal basis for his claim about photographs taken from a train.