This article takes a look at what might be a bit of a current trend to sometimes treat photographers as suspects. There are some helpful links to sites that set out the legal position regarding photography in public places.
In response to reports of overzealous demands by police for photographers to delete images or hand over memory cards, the Nottinghamshire Police guidelines state:
Police officers do not have the authority to prevent a person taking a photograph or to confiscate cameras or film, and such conduct could result in criminal, civil or diciplinary action.
There's an excellent 'print your own' guide to UK photographers rights here.