A legal challenge to prevent the Metropolitan Police from using facial recognition cameras has been launched.
Civil liberties group Big Brother Watch has joined forces with Baroness Jenny Jones to ask the government and the Met to stop using what they deem "dangerously authoritarian" facial recognition cameras.
In what is thought to be the first legal challenge of its kind, the use of real-time facial recognition cameras by the Met is being contested.
The controversial cameras have been used by the Met for two years at Nottingham Carnival and at Remembrance Sunday.
Big Brother Watch and Baroness Jones claim that the police lack a legal basis to use the technology and that it breaches fundamental rights protecting privacy and freedom of expression.
The civil liberties group describes the use of the cameras as a "lawless growth of Orwellian surveillance".
A legal letter sent to the Home Office, seen by Sky News, asked Home Secretary Sajid Javid to withdraw support for the technology or to demonstrate that facial recognition is being used proportionately and legitimately in reference to the European Convention of Human Rights.
If this request is ignored, the group says it will take the case to court.
A separate legal letter sent to Met Police Commissioner Cressida Dick, also seen by Sky News, sets out that the group and Baroness Jones see "the use of AFR (automated facial recognition) technology is unlawful".
The letter asks them to stop using the technology or to answer a number of questions around the use of the cameras.
Silkie Carlo, director of Big Brother Watch, told Sky News: "We view this technology as a really dangerous breach of fundamental rights.
"The police just don't have the legal basis to use this technology and that sets a really dangerous precedent – especially as the Home Office has spent millions of pounds on the police using it when they haven't even attempted to get a legal basis for the technology. It's a shambles."
The Met has not published a policy on their use of the technology, nor has it provided much detail on the watch list assembled by the force.
Last year, Sky News revealed that a trial of facial recognition equipment at Notting Hill Carnival resulted in roughly 35 false matches and an "erroneous arrest".
Sky News also revealed in 2017 that more than 20 million facial recognition images are being held by police in the UK.
The Met has said it will not use the technology at this year's Notting Hill Carnival.
It is understood the force intends to roll out a further seven tests of the cameras.
Baroness Jones, whose photo is thought to be held on a state database after being stored on the Met's "domestic extremism" watch list, said she was concerned about the impact of the technology on her ability to carry out her work.
In a statement to Sky News, she said: "As part of my parliamentary work I attend public events and demonstrations, meeting whistleblowers and campaigners who may not be able to meet me if police surveil events with facial recognition.
"Police use of this technology has no legal basis, and infringes peoples rights and civil liberties."
Ms Carlo said: "The lawless growth of this Orwellian surveillance technology must be stopped. Facial recognition cameras are dangerously authoritarian, hopelessly inaccurate, and risk turning members of the public into walking ID cards.
"The UK already has the most extensive CCTV of any democracy in the West. The prospect of facial recognition turning those CCTV cameras into identity checkpoints like China is utterly terrifying."
MPs have criticised the government for being five years late in producing the biometrics strategy it had promised would address issues, including the management of photos of innocent people.
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Earlier this month, biometrics commissioner Professor Paul Wiles warned the police use of biometric technologies is "running ahead of the law".
A spokesperson for the Home Office previously said: "Analysis of images plays a critical role in helping the police to protect the public. When doing so it is important that the police act legally, ethically, and transparently."
The Home Office says it is now considering the select committee's report and is "committed to publishing the Biometrics Strategy in June".