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Police forces across the UK effectively campaigned to use a face scanning system known to be discriminatory against women, young people, and individuals from ethnic minority groups, after complaining that a less biased version generated a reduced number of investigative leads.

The Technology in Practice

British police use the police national database (PND) to conduct retrospective facial recognition searches. This process entails matching a “probe image” of a person of interest against a repository of more than 19 million mugshots to identify possible hits.

Admitted Bias

The UK interior ministry admitted last week that the system was flawed. This acknowledgment came after a review by the National Physical Laboratory (NPL) determined it incorrectly matched Black and Asian people and women at significantly higher rates than white men. The Home Office said it “had acted on the findings”.

“This raises the question of whether facial recognition only becomes useful if users tolerate discrimination in race and sex. Operational ease is a weak argument for disregarding basic freedoms.”

Known Issue

Official papers show that this bias has been known about for more than a year. Furthermore, police forces lobbied to reverse an earlier ruling that was designed to mitigate the problem.

Police bosses were informed of the system's bias in September 2024. The Home Office-commissioned laboratory study found the system was had a higher probability to produce false positives for images depicting females, individuals of Black ethnicity, and those under 40 years old.

A Reversed Decision

In reaction, the national police leadership body mandated that the confidence threshold required for potential matches be increased to a point where the disparity was significantly reduced.

However, this decision was reversed the next month after forces complained that the adjusted system was generating a lower number of “useful lines of inquiry”. Internal records show the stricter setting cut the proportion of queries that yielded possible identifications from over half to a mere 14%.

Profound Inequalities

Although the Home Office and NPCC refused to say what threshold is currently used, the latest NPL study discovered the system could produce incorrect matches for women of Black heritage almost 100 times more often than for white women at certain settings.

The Home Office commented on these results: “The testing found that in a specific scenarios the algorithm is more likely to incorrectly include some population segments in its match reports.”

Balancing Utility and Fairness

Describing the effect of the temporary raise to the system's confidence threshold, the NPCC documents state: “This adjustment greatly lessens the effect of bias across protected characteristics of ethnicity, generation and gender but had a significant negative impact on police efficiency”. The documents further note that forces argued that “a previously useful tool returned outcomes of limited benefit”.

Broader Rollout Plans

Meanwhile, the government has launched a two-and-a-half-month public review on its plans to expand the use of facial recognition technology. Policing minister Sarah Jones has described the technology as the “biggest breakthrough since DNA matching”.

Expert and Oversight Concerns

The chair of a police oversight board, head of the independent scrutiny and oversight board for the police race action plan, said: “We observed scant consideration through race action plan meetings of the facial recognition rollout even with clear relevance with the plan’s concerns.

“These revelations demonstrate yet again that the pledges to combat discrimination policing has made through the equality initiative are failing to be integrated into wider practice. Independent assessments have warned that new technologies are being implemented in a context where racial disparities, weak scrutiny and poor data collection continue to exist.

“All deployment of facial recognition must adhere to rigorous official guidelines, be subject to external review, and prove it diminishes rather than exacerbates ethnic bias.”

Official Statement

A Home Office spokesperson stated: “We treat the findings of the study with utmost gravity and we have implemented changes. A updated software has been externally evaluated and acquired, which has demonstrated no measurable discrimination. It will be trialled early next year and will be subject to evaluation.

“Our priority is ensuring public safety. This revolutionary tool will support police to apprehend and prosecute offenders. There is officer review in every step of the process and no arrest or charge would be taken without specialist personnel meticulously examining the output.”