Here is another useful resource put together by a former solicitor http://4020.net/words/photorights.php
The general gist is that street photography is legal - you can take and sell pictures of people without their permission. Obviously in some specific locations there may be restrictions and being legally in the right doesn't mean someone wont punch you on the nose if you keep taking pictures when they ask you not to.
....It more or less stated that unless denied by police , security and people of authority, you are free to take photographs in public places but also asks you to respect the rights of people who request not to have their photo taken out of common courtesy.
As the above link points out photography isn't a crime and as such the police have no right to stop you taking photographs in public (unless you are directly
interfering in their work). Neither do security people for nearby buildings or other people of authority, whose authority actually doesn't extend to stopping you from doing things that are legal. Nor is it suspicious and as such isn't grounds for the police to search you.
I am learning photo graphee - see the results at www.danmarchant.com