Met Police officers are to start wearing cameras on their uniforms as part of plans to boost transparency and accelerate convictions.
The cameras are designed to capture evidence at crime scenes.
A trial will see 500 devices distributed to officers across 10 London boroughs. Firearm officers will also use them in their training.
But, Jack Hart from The Freedom Association says the move means "everyone is under suspicion".
The pilot scheme comes following criticism of the force over the death of Mark Duggan at the hands of armed officers.
The death of Mr Duggan, 29, in Tottenham, north London, in August 2011, sparked riots in the area that later spread across England.
'Speeds up justice'
Camden Borough is the first to start using the cameras, with further trials in Barnet, Bexley, Bromley, Brent, Croydon, Ealing, Havering, Hillingdon and Lewisham.
Officers will store material from each incident and keep it on file for a month unless it is required for evidential purposes.
These devices will be shared amongst the Met's 31,000 officers.
A spokesman said the force first became involved with body cameras in 2007 when it worked with the College of Policing.
Met Commissioner Sir Bernard Hogan-Howe said: "Our experience of using cameras already shows that people are more likely to plead guilty when they know we have captured the incident.
"That speeds up justice, puts offenders behind bars more quickly and protects potential victims."
The Scotland Yard chief said video was a "compelling piece of evidence" and would help record situations which were previously "really hard to capture in writing", such as a frightened child at the scene of a domestic violence incident.
He also said the "mere presence of this type of video can often defuse potentially violent situations".
"I believe it will also 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," Sir Bernard continued.
"That has to be in both our own and the public's interest."
The force said officers taking part in the pilot must comply with guidelines about when cameras are to be used, but that they will not be permanently switched on and people would be informed if they were being filmed.
The commissioner added: "[We will] only put it on when we know there's a an incident running.
"If the victim wants it to be turned off it will be turned off, but the suspect doesn't have that right."
The debate over the more widespread use of body-worn cameras by British police comes after a jury at the inquest into Mr Duggan's death concluded in January that he had been lawfully killed by Met marksmen - a conclusion which prompted outrage from his family and supporters.
None of the officers involved in the incident in London was wearing body cameras.
However, Mr Hart said: "No police officer will have their body-worn camera on continually because of the sheer amount of data storage required; which will open continual debates about whether or not a camera was deliberately turned off.
"To create a situation where both police officers and the public feel constantly under suspicion is not sensible and undermines trust in all sectors of society."
Some forces, including Hampshire, already use the cameras. They were first used by Devon and Cornwall Police in 2006.
Earlier this week, Bedfordshire Police said 60 body cameras would be used by front-line officers following a successful trial.