Most of London's police officers will be issued with body-worn video cameras as part of the biggest rollout of the technology so far.
The project will see the majority of uniformed officers in the capital equipped with cameras by the end of March 2016 - the largest such deployment in a city anywhere in the world, according to London mayor Boris Johnson.
The introduction of the cameras for officers across London's Metropolitan police force will follow the completion of a trial this summer. The Met said that so far the pilot project has seen cameras both reducing complaints and increasing the number of early guilty pleas.
The trial - which has been running since last year - uses around 1,000 body cameras across 10 boroughs, as well as armed response teams. Around 6,000 videos are uploaded per month and if the clips are not being used as evidence, the footage is automatically deleted after 30 days.
The camera used in the trial is attached to the officer's body armour, and is not permanently switched on but activated by when the wearer either presses a button on the body of the camera or slides a switch across the top. When it is on, a red flash appears.
Feedback from officers so far suggests the devices are most valuable "where trust is key and police behaviour is under scrutiny", said the Mayor's office: for example, in 'stop and search' situations, and where early evidence and victim testimony is critical, such as in cases of domestic abuse.
Metropolitan Police commissioner Sir Bernard Hogan-Howe said: "For too long our equipment has lagged behind the technology almost everyone has in their pockets to capture events as they unfold."
"Soon, more of our officers will be able to make a record of the very challenging circumstances they are asked to deal with on a daily basis and then demonstrate, more effectively, the reality of policing our capital. It will also improve public scrutiny of how we carry out our role. That is a vital part of being an accountable police officer. It is also an essential tool in gathering evidence of offences."
In an attempt to allay fears about encroaching surveillance, the authorities plan to explain to Londoners how the technology works and where and when they might encounter it. The London policing ethics panel is working on guidelines around how officers use the cameras.
The Mayor's office will begin the procurement process for the 20,000 new devices in the coming weeks: the project is being funded by the sale of under-used police buildings.
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