This cartoon film by Gemma Atkinson should act as a cautionary tale for any would-be street photographers, whether they are professionals or amateurs, who are inclined to photograph or film the police enacting their duties on the streets.
The web site also includes links to useful information about your rights as a street photographer. Of particular interest is the Metropolitan Police’s advice on photography under The Terrorism Act 2000 (Photography and Section 44 of the Terrorism Act 2000).
I have printed this, and will carry it with me in my equipment bag, so that I can consult t if challenged. It may help to defuse a difficult situation, and potentially save a lot of subsequent, unnecessary hassle.
See also: PhotographerNotATerrorist