The creeping rise of pseudo-public space in London has started to impact on quite a few street photographers many of whom have blogged about it
Personally I’ve never had a problem so far; my camera setup is quite discrete so I think I get mistaken for a tourist most of the time!
On the one occasion I was approached I carried on as though I hadn’t heard the security guard and then walked on. They didn’t say anything else and left me to get on with taking a few more photos
You can read an interesting article in the Guardian newspaper which gives a lot more detail on this new phenomenon here