The UK government's approach to deleting custody images of innocent people – in that it only scraps them on request – is unacceptable and possibly illegal, MPs have said.

In a report published today, the House of Commons Science and Technology Committee slammed the Home Office's attitude to its custody image database, and the weaknesses in police IT systems that stop the retention of these images falling in line with the law.

There are now around 21 million shots of faces and identifying features like scars or tattoos in the custody image database. This includes images of people who haven't been charged with a crime, because – unlike the UK's DNA or fingerprint databases – these images are only removed if someone requests it.

This is despite a 2012 High Court ruling that said keeping images of presumed innocent people on file was unlawful, and that there must be a distinction between those who are convicted and those who aren't.

However, rather than setting up an automatic deletion process – which happens for DNA and fingerprints – the Home Office said that unconvicted people would have to request that their images be deleted.

It has since said that it is not technically possible to automatically delete images, because the national and local databases don't talk to each other – it is impossible to automatically link someone's custody status with their image, and all image deletions must be done manually.

Minister Susan Williams told MPs last month that trying to clean the innocent people off the central database would be too costly to justify, but said a new platform being developed under the National Law Enforcement Data Programme would "resolve this in the medium term".

However, the MPs say this is "unacceptable", arguing that it raises specific ethical problems because unconvicted people may not know they can apply for their images to be deleted, and because these people shouldn't have less protection than those who have given fingerprint or DNA samples.

"The government must ensure that its planned IT upgrade is delivered without delay to introduce a fully automatic image deletion system for those who are not convicted," the report said.

"If there is any delay in introducing such a system, the Government should move to introduce a manually processed comprehensive deletion system as a matter of urgency."

The committee said the government should set out which of these routes it will take in the long-overdue Biometrics Strategy, which is due for publication next month. In addition, it should include the Home Office's assessment of the lawfulness of its existing deletion-on-application solution.

In addition, the strategy should consider further refining the oversight architecture relating to the collection, use and retention of facial images, including the management and regulation of image databases, with the committee mooting a dedicated regulator or extending the biometrics commissioner's remit.

The report also briefly considers the use of facial-recognition kit – a controversial and reportedly inaccurate technology that has been repeatedly rolled out by police forces in the capital and South Wales to little effect.

Among the MPs' particular concerns are the potential for such technology to be biased or discriminatory, and it should not be used beyond the existing pilots until these issues have been fully resolved.

They call for the Biometrics Strategy to include an undertaking so that parliament is given a chance to debate the further use of the technology, saying that it should be ministers and parliament – not the police – that makes the final decision on wider deployment.

The MPs sum up the report – which also considered forensics, calling for a review of the 2016 forensics strategy – by saying that there is "an urgent and significant need for action on the governance and oversight" of both issues.

"This is vitally important because these disciplines, and the way their techniques and data are used, are at the heart of our courts system and underpin essential confidence in the administration of justice," it said. ®