London's Metropolitan Police yesterday began issuing 500 body cameras to officers in a pilot programme to improve evidence-gathering and monitor officers' behaviour.
The cameras will be used at first by officers dealing with domestic violence and public-order offences.
They will also be used when officers carry out contentious activities such as stopping and searching suspects without a warrant, the police said.
"Body-worn video will not only help us fight crime and support victims but help the Met to be more accountable," Commissioner Bernard Hogan-Howe said.
"Video captures events in a way that can't be represented on paper in the same detail and it has been shown the mere presence of this type of video can often defuse potentially violent situations without the need for force to be used."
The cameras, made by Taser International, will be attached to officers' body armour and will only be switched on when incidents occur, police said. They will be given to officers in 10 of London's 32 boroughs and the results of the study will be evaluated by Mayor Boris Johnson's office and police trainers before any decision is taken to order more.
"I believe it will show our officers at their best, dealing with difficult and dangerous situations every day but it will also provide clearer evidence when it's been alleged that we got things wrong," Hogan-Howe said.
"That has to be in both our own and the public's interest."
The shooting of Mark Duggan by Met Police officers in August 2011 sparked riots across the United Kingdom. A jury in January this year said Duggan had been "lawfully killed" after hearing conflicting evidence of his interaction with the police.