There is no law stopping anyone filming in a public place, so if you are on the streets you can film without asking permission – the Metropolitan Police’s own guidelines (adopted by all police forces in Britain) make clear that “police have no power to stop them filming or photographing incidents or police personnel”.
There is a law – Section 58A of the Terrorism Act 2000 – that says police officers can stop you filming them if they believe that the video will be used for purposes of terrorism. However, police guidelines state that:
“it would ordinarily be unlawful to use section 58A to arrest people photographing police officers in the course of normal policing activities… An arrest would only be lawful if an arresting officer had a reasonable suspicion that the photographs were being taken in order to provide practical assistance to a person committing or preparing an act of terrorism”.
This does not apply when you stop to film the police stopping and searching people.