Hundreds of police officers will be fitted with body-worn cameras in a pilot scheme which could see them rolled out across the country.
Five-hundred officers across eight London boroughs will wear the cameras from March this year, in what will be the largest ever pilot of body-worn cameras.
The scheme is likely to be greeted with scepticism from some civil liberties campaigners.
A study last year estimated that there are already around six million CCTV cameras in operation across the UK.
However, the move has long been called for by campaigners who believe it could stop future miscarriages of justice.
The campaign was heightened after the death of Leon Briggs in police custody last year.
Campaigners for Leon today welcomed the move but warned that confidence could be undermined if officers are free to turn off the cameras.
"All police officers in all interactions with the public [should] wear body worn cameras and they should be recording during those interactions," Michael Doherty, of Justice for Leon told the London edition of the Politics Show, which broke the story today.
"Technology really is going to start to hold police officers to account, but it won't hold them to account if they have the discretion to turn them off when they choose."
London's Deputy Mayor for Policing said he was not in favour of leaving the cameras recording permanently, prompting fears that officers could be free to turn them off at will.
Asked whether he would like to see them recording permanently he replied: "No… having the camera on all the time means you have to work out how much of that you store, how long you store it. I think you have to be focused."
Labour's Diane Abbott also warned against giving officers the powers to turn them off.
"You've got to have a protocol. Police can't just shut the cameras off when it suits them."
Body-worn cameras are already in use in some parts of the country. However, officers can currently only turn them on in anticipation of an incident.