Geektastic:
It's perfectly legal to take photographs of people in public places without their consent, however, provided said images are not indecent.
It would not be legal to use those images for anything other than editorial use unless you obtained Model Consent.
It would not be legal (generally) to take images of a person in a place where they had a reasonable expectation of privacy (e.g. in their own back yard) but someone standing on a street in public? They may not like it but that isn't relevant to the legality of doing it.
Try standing in front of a girl's school with a camera and photographing the children as they come out and see how far you get.