Lord Carlile QC, who reviews anti-terror legislation for the government, said officers should not use force or threats against photographers to make them delete images.

Section 58A of the Counter-Terrorism Act, which came into force in February, bans photographers from taking pictures of the police if the photographs could be useful to terrorists.

Lord Carlile said this was a "high bar" and should not be used to interfere with day-to-day photography.

The NUJ organised a gathering of photographers outside the Metroploitan Police HQ on the day the law came into force.

• Video: Photographers beseige Scotland Yard 

In his annual review of anti-terror laws, Lord Carlile said: "It should be emphasised that photography of the police by the media or amateurs remains as legitimate as before, unless the photograph is likely to be of use to a terrorist. This is a high bar.

"It is inexcusable for police officers ever to use this provision to interfere with the rights of individuals to take photographs.

"The police must adjust to the undoubted fact that the scrutiny of them by members of the public is at least proportional to any increase in police powers - given the ubiquity of photograph and video-enabled mobile phones.

"Police officers who use force or threaten force in this context run the real risk of being prosecuted themselves for one or more of several possible criminal and disciplinary offences."

Jeremy Dear, NUJ General Secretary, said: “Like Lord Carlile we have been very concerned about the heavy -handed action by police who see the anti-terror laws as a licence to harrass photographers.

“This is an unjustified attack on civil liberties, press freedom and the right of freelance photographers to earn a living.

“We welcome Lord Carlile’s warning to police officers and trust that the Home Office and Chief Constables will make sure officers on the ground are made aware of his strong words.”

• Union fights for photographers' rights

18 June2009