A few days before Christmas 2017, I stepped out of my office on to Cardiff high street to grab some lunch. Among the crowd of flustered last-minute shoppers, I was captured.

Without my consent or knowledge, the police had scanned my facial features, creating a “biometric” map of my face – as unique to me as my fingerprint or DNA.

I was not suspected of a crime and was not on any criminal “watchlist” – I was just one of thousands of people who happened to be walking in the view of the police’s facial recognition cameras that day.

A few months later, I saw the cameras again at a peaceful protest against the Cardiff Arms Fair. Along with hundreds of other protesters, I was being monitored by a technology more invasive and chilling than any surveillance tool I had seen on Britain’s streets before.

There may have been as many as 50 deployments across South Wales, so I must be one of hundreds of thousands of people who have had their faces scanned while innocently going about their daily lives. The “trial” is open ended, with no publicly available criteria to measure it. South Wales police initially used the technology at events with large crowds, such as the 2017 Champions League final, but now use it regularly as part of everyday policing.

South Wales police said last year that its use of this technology was “lawful and proportionate”. However there has been no public consultation, no parliamentary debate, no warning that this invasive new surveillance tool is being rolled out.

I felt I had to do something to stop the police from monitoring us in this way, and bring it to public attention. That’s why the legal case that Liberty and I have brought will argue this week that, by scanning and capturing the biometric data of all passersby in their use of facial recognition technology, the police are violating our right to privacy.

To make matters worse, studies have shown that this technology remains highly ineffective, particularly when applied to women and people from minority ethnic communities – this means those people are more likely to be stopped by police owing to an inaccurate match. So we’ll also be arguing that the use of facial recognition breaches police duties under equality laws.

This case is crucial. While South Wales police are pioneering this technology, funded by the UK government, other forces are exploring facial recognition and the Metropolitan police have trialled it. This case sends a clear message to other police forces and the government that there are grave concerns that this technology is unlawful and has no place on our streets.

Because the law lags behind technology, facial recognition currently exists in a regulatory vacuum, so at present it is being used in ways that undermine public confidence in the police and the systems they avail of. The creeping use of facial technology forces us to be wary with regard to where we go and with whom, what we do, and whether we protest. It fundamentally changes our public spaces, and our relationship to the state.

And for anyone who says “if you’ve got nothing to hide you’ve got nothing to fear”, the answer is simple: we fought for many years to win the rights and freedoms that protect us from authoritarian state rule. These freedoms ensure that in Britain, policing is by consent only – no one wants that to change. So we must resist intrusions into those freedoms whenever they occur.

It is an intrusive invasion of our privacy and a discriminatory tool that we believe will increase the over-policing of minority groups. That’s why I’m challenging it in court. We hope the court agrees, and ends this use of facial recognition.

• Ed Bridges is a Cardiff resident and civil rights campaigner