Planning on heading to Cardiff's Principality Stadium to watch the Uefa Champions League finals on 3 June? You may be among the thousands to have your face scanned as part of a massive security experiment by the British police. The South Wales Police will pilot a new facial recognition surveillance system at Europe's biggest sporting event.

Every one of the nearly 170,000 fans expected to show up at the Champions League finals will have their face scanned, processed and matched against a police database of 500,000 "persons of interest". The move has reportedly garnered criticisms from fans and raised privacy concerns.

UK government's surveillance camera commissioner Tony Porter told Motherboard that incidents such as the recent Borussia Dortmund bus bombing have propelled law enforcement to adopt AFR (Automated Facial Recognition) technology. Porter also said that the police must use the technology in compliance with the surveillance camera code of practice.

"My office has been in touch with South Wales Police to help them ensure that when deploying AFR they are complying with the code [of practice]," Porter told Motherboard.

"I have seen the use of AFR increase [over] the past few years and a recent report by the National Institute of Standards and Technology indicated that facial recognition is a difficult challenge," Porter added. "Getting the best, most accurate results for each intended application requires good algorithms, a dedicated design effort, a multidisciplinary team of experts, limited-size image databases, and field tests to properly calibrate and optimize the technology."

AFR technology comes with its own limitations. According to a recent NIST Face in Video Evaluation program report, AFR can only accomplish accurate facial recognition in controlled environments.

Privacy advocates are reportedly concerned about the limitations of the technology as well as the lack of clear regulations. Rachel Robinson, policy director at human rights and civil liberties campaign organisation Liberty told Motherboard, "The chasm between the increasingly advanced surveillance technology rolled out by police and the lack of legal safeguards for the public is growing wider and more alarming all the time."

While Robison acknowledged that there are times when CCTV security measures become necessary, she added that "instantaneous facial recognition technology with the potential to identify anyone in a crowd of thousands, alongside ongoing police storage of huge numbers of innocent people's photographs, is a seriously intrusive combination."

However, despite concerns about the technology, the focus in the use of AFR appears to be escalating among law enforcement. Commenting on the future use of AFR by police, Porter said, "I foresee this continuing. In terms of additional applications I can see it linking in with other technology such as body worn video, being used along other databases and so on."