The Metropolitan Police Service’s approach towards photography in public places is a subject of regular debate.
We encourage officers and the public to be vigilant against terrorism but recognise the balance between effective policing and protecting Londoners and respecting the rights of the media and the general public to take photographs.
Guidance around the issue has been made clear to officers and PCSOs through briefings and internal communications. The following advice is available to all officers and provides a summary of the Metropolitan Police Service’s guidance around photography in public places.
Freedom to photograph/ film
Members of the public and the media do not need a permit to film or photograph in public places and police have no power to stop them filming or photographing incidents or police personnel.

Further information from -

 http://www.met.police.uk/about/photography.htm