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Police forces across the UK effectively campaigned to use a face scanning system known to be biased against females, young people, and individuals from ethnic minority groups, following complaints that a less biased version produced a reduced number of potential suspects.

The Technology in Practice

UK forces use the national police database to conduct retrospective facial recognition searches. This procedure entails matching a “probe image” of a person of interest against a repository of more than 19 million mugshots to identify potential matches.

Admitted Bias

The Home Office admitted last week that the system was flawed. This admission came after a review by the National Physical Laboratory (NPL) found it misidentified Black and Asian people and females at much greater frequency than white men. The Home Office said it “took steps on the findings”.

“This raises the issue of whether this technology only becomes useful if users tolerate discrimination in race and sex. Convenience is a weak argument for disregarding fundamental rights.”

Long-Standing Problem

Official papers show that this discriminatory flaw has been known about for more than a year. Furthermore, police forces argued to overturn an earlier ruling that was intended to mitigate the problem.

Senior officers were informed of the system's bias in late 2024. The Home Office-commissioned laboratory study concluded the system was had a higher probability to suggest incorrect matches for images depicting females, individuals of Black ethnicity, and those aged 40 and under.

A Reversed Decision

In response, the National Police Chiefs’ Council (NPCC) ordered that the accuracy setting required for possible hits be increased to a point where the disparity was significantly reduced.

However, this decision was reversed the following month following complaints from police that the adjusted system was producing a lower number of “investigative leads”. NPCC documents show the higher threshold cut the proportion of searches resulting in possible identifications from over half to a just under 15%.

Severe Disparities

Although the authorities declined to specify what threshold is currently used, the latest NPL study found the system could produce incorrect matches for Black women nearly a hundred times more frequently than for white women at specific configurations.

The Home Office stated on these results: “Our evaluation found that in a limited set of circumstances the algorithm is has a greater tendency to wrongly flag some demographic groups in its match reports.”

Operational Effectiveness vs. Bias

Describing the effect of the brief increase to the system's confidence threshold, the NPCC documents note: “The change significantly reduces the effect of discrimination across protected characteristics of race, age and sex but had a substantially detrimental effect on operational effectiveness”. The papers add that police units complained that “a once effective tactic returned results of questionable value”.

Wider Implementation Proposals

Meanwhile, the government has opened a ten-week public review on its proposals to widen the use of facial recognition technology. The minister for police the relevant minister has described the tool as the “biggest breakthrough since DNA matching”.

Criticism from Advisors and Monitors

Abimbola Johnson, chair of the advisory panel for the police race action plan, said: “There was very little discussion in equality strategy sessions of the technology deployment despite clear relevance with the strategy's goals.

“This disclosure show once again that the pledges to combat discrimination the police has undertaken via the race action plan are not being translated into broader operations. Independent assessments have cautioned that new technologies are being rolled out in a context where racial disparities, inadequate oversight and faulty information gathering continue to exist.

“All deployment of facial recognition must meet strict national standards, be subject to external review, and prove it reduces rather than exacerbates racial disparity.”

Official Statement

A Home Office spokesperson said: “The Home Office takes the conclusions of the study with utmost gravity and we have implemented changes. A new algorithm has been externally evaluated and acquired, which has no statistically significant bias. It will be trialled in the coming months and will be subject to further assessment.

“Our priority is protecting the public. This revolutionary tool will support officers to put criminals and rapists behind bars. There is human involvement in each stage of the procedure and no arrest or charge would be pursued without trained officers carefully reviewing the results.”