The worst place for me is the city square mile, especially along southbank. A few weeks ago i was opposite houses of parliament trying to take a pano, half way through i was stopped by 2 community officers.
One officer asked what i was doing, asked what i was then taking pictures of, was i professional photographer, and then wanted to see the pictures. The whole thing was self explanatory and not needed in my opinion. Its annoying cause during the process other people around think your shifty and you feel guilty without doing anything incriminating.