The Home Office is facing mounting pressure to explain why there is still no publication date for its biometrics strategy, nearly four years after it was supposed to be published.

The government promised to provide a framework guiding the police’s use of facial recognition imagery and other forms of biometrics data by the end of 2013.

But the minister for countering terrorism, Baroness Susan Williams, admitted last month that the strategy was now not expected to be published until next year.

In light of the admission, the chair of the science and technology select committee, MP Norman Lamb, wrote to the minister yesterday to seek “full clarity” on the reasons for the “continuing delay”.

“What aspects of the proposed strategy has caused particular problems?” he asked. “It would be helpful to know when a draft first reached ministers for consideration.”

“It would be helpful also, not least for the Committee in planning its future scrutiny work, to have a more precise estimate – beyond ‘next year’ – for when the Strategy will appear,” he added.

In an interview with NS Tech in September, Lamb warned that the government’s failure to publish the framework “massively increases the risk of abuse”. He said it was “extraordinary” that police forces are starting to apply facial recognition technology “in a policy-free vacuum”.

The technology has gained popularity among police forces across the country. In June, South Wales Police cross-referenced CCTV footage with 500,000 custody images to surveil crowds at the Champions League final. Two months later, the Met deployed the technology at Notting Hill Carnival, in a move described as discriminatory by civil liberties groups.

A member of staff from the human rights organisation Liberty who observed the carnival operation said the technology led to at least 35 false positives, five people being unduly stopped and one wrongful arrest.

The Met denied the individual had been arrested, but admitted he had been “dealt with for the offence” before being stopped.

The Home Office had been due to publish a joint forensics and biometrics strategy by the end of 2013. But in March 2016, it published the forensics strategy without the biometrics component.

In the same month, it confirmed in a Freedom of Information request that the biometrics component was “in the final stages of completion”.

Biometrics commissioner Paul Wiley noted in his annual report earlier this year that people are at risk of being unduly targeted by the police because their images are stored in a vast facial recognition database.

The National Police Database now contains at least 19 million custody images, hundreds of thousands of which belong to people who were later acquitted or never charged with a crime, according to Wiles.

The retention of innocent people’s facial images was deemed unlawful by a court more than five years ago, but a Home Office review published in February said police should delete images only if the subject asks them to do so.

Wiles said it remained to be seen how many people would take up the opportunity. “The evidence from a similar application process to the police, to delete [Police National Computer] and biometric records, is not encouraging,” he wrote.

The commissioner also warned that there is no independent oversight of the police’s retention of secondary biometric data such as facial images and voice recordings.

“This whole process is in the hands of the police itself,” he said. “What we’ve got is a legislative deficit. I think that’s very worrying because if we’re not careful the public will lose confidence in the police.”