Thousands of frontline officers in the country's biggest police force will be equipped with body-worn cameras over the coming months.
Scotland Yard began a large-scale deployment of Body Worn Video (BWV) to more than 22,000 Metropolitan Police officers on Monday, the largest rollout of its kind in the world.
Mayor of London Sadiq Khan and the Met's commissioner Sir Bernard Hogan-Howe joined officers wearing the cameras on their first beat in Lewisham, south-east London.
Cameras will be issued to London's 32 boroughs and to a number of frontline specialist roles, including overt firearms officers. Undercover marksmen are currently unable to use the devices because they are too large.
Last month a survey by the Press Association of forces across the UK revealed a patchy approach to introducing the cameras, with North Yorkshire Police having no plans to adopt body-worn video, and forces including West Mercia and Devon and Cornwall having problems with the technology.
In contrast a string of other forces including the Met, Greater Manchester, Leicestershire, Surrey, City of London and North Wales are among those with plans to use cameras.
Scotland Yard announced it would introduce the devices in the wake of the fatal shooting of Mark Duggan, whose death at the hands of a police marksman in 2011 sparked a wave of unrest that spread across the country.
Sir Bernard, who is Britain's most senior police officer, said: "It holds us to account, because if the officer does a great job we will capture that and if they don't do a good job we should capture that.
"What we found in the pilot is they capture really powerful evidence which leads to more guilty pleas. It's led to less complaints and generally the public have accepted it.
"What we are doing is catching up with society rather than being more intrusive."
The cameras record constantly but only permanently save the footage starting 30 seconds before officers press record, because of privacy considerations and data storage.
Sir Bernard said that if an officer repeatedly failed to record footage, force bosses would "inquire into that".
Labour mayor Mr Khan said: " It makes it easier for the police to obtain evidence and leads to faster justice. It also leads to more transparency and accountability in the police force.
"By the end of next summer every police officer that comes into contact with the public will have a body-worn video."
A red light will flash on the camera when it is recording and members of the public will be told as soon as practical that they are being recorded. They can ask for a copy of the footage using a Freedom of Information Act request.
In November 2015, the Mayor's Office for Policing and Crime (MOPAC), awarded a three-year contract worth £3.4 million to Axon Public Safety UK Limited to supply the Met with 22,000 cameras.
Last month, a study by the University of Cambridge found a 93% decrease in complaints made against officers clearly wearing body cameras.