Stop that - no photography allowed!

It's happened again! I am getting really tired of security people, and others, trying to tell me that photography is not allowed. In this case I was with two friends taking photographs from the canal towpath outside the Lostock Works of Brunner Mond. Then this guy arrives in his little white van, crosses the bridge and comes up the path shouting that we must stop immediately and that photography is not allowed. After I asked him who he was and why no photos allowed he said because Brunner Mond didn't allow it. I suggested that Brunner Mond had no say in whether I could take photos from a public place and he went off to get the police. Funnily enough no police arrived and when we saw him later he was still insisting that we could not take photos. I wonder how many people are put off by this sort of intimidation.