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Police forces across the UK effectively campaigned to use a face scanning system known to be biased against women, youths, and individuals from minority ethnic backgrounds, after complaining that a less biased version generated a reduced number of potential suspects.

How the System Works

British police utilize the national police database to carry out searches using historical face recognition. This procedure involves matching a “probe image” of a person of interest against a database of over 19 million mugshots to identify possible hits.

Admitted Bias

The Home Office conceded last week that the system was biased. This acknowledgment followed a review by the National Physical Laboratory (NPL) determined it misidentified Black and Asian people and females at significantly higher rates than white men. The ministry said it “had acted on the findings”.

“This raises the issue of whether this technology only becomes useful if users tolerate discrimination in ethnicity and gender. Convenience is a poor argument for disregarding basic freedoms.”

Known Issue

Official papers reveal that this bias has been known about for over twelve months. Furthermore, police forces lobbied to reverse an earlier ruling that was designed to mitigate the problem.

Police bosses were notified of the algorithmic discrimination in late 2024. The government-ordered NPL review concluded the system was more likely to produce false positives for photos of women, individuals of Black ethnicity, and those aged 40 and under.

A Policy U-Turn

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

However, this directive was overturned the next month after forces complained that the modified technology was producing a lower number of “investigative leads”. NPCC documents show the higher threshold cut the proportion of searches that yielded potential matches from over half to a just 14%.

Severe Disparities

Although the authorities refused to say what threshold is now in operation, the latest NPL study found the system could generate false positives for Black women nearly a hundred times more often than for Caucasian women at specific configurations.

The ministry commented on these results: “The testing found that in a limited set of circumstances the software is more likely to wrongly flag some demographic groups in its match reports.”

Balancing Utility and Fairness

Outlining the effect of the temporary raise to the system's confidence threshold, the NPCC documents note: “This adjustment significantly reduces the effect of discrimination across protected characteristics of ethnicity, generation and gender but had a significant negative impact on operational effectiveness”. The documents add that forces complained that “a previously useful tool now delivered results of questionable value”.

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 the relevant minister has labeled the tool as the “most significant advance since genetic fingerprinting”.

Criticism from Advisors and Monitors

Abimbola Johnson, head of the advisory panel for the police race action plan, commented: “There was scant discussion through race action plan meetings of the technology deployment even with clear relevance with the plan’s concerns.

“This disclosure demonstrate yet again that the pledges to combat discrimination the police has undertaken through the race action plan are not being translated into broader operations. Our reports have warned that new technologies are being implemented in a landscape where ethnic inequalities, weak scrutiny and poor data collection already persist.

“Any use of this technology must meet strict national standards, be independently scrutinised, and prove it reduces rather than exacerbates ethnic bias.”

Home Office Response

A government representative said: “The Home Office takes the findings of the study seriously and we have already taken action. A new algorithm has been independently tested and acquired, which has demonstrated no measurable discrimination. It will be trialled in the coming months and will be subject to further assessment.

“The foremost aim is protecting the public. This revolutionary tool will assist officers to apprehend and prosecute offenders. There is human involvement in each stage of the procedure and no further action would be pursued without specialist personnel meticulously examining the results.”