Ministers face a parliamentary inquiry over the storing by police of 20 million mugshots – including of many people not convicted of any crime – after a senior MP warned the practice raises “fundamental civil liberty issues”.

A Commons committee is poised to launch the probe after running out of patience with the Government, which has failed to act on the controversy almost six years after it was ruled unlawful by the High Court.

The court warned of the “risk of stigmatisation of those entitled to the presumption of innocence”, adding that it would be particularly harmful in the cases of children.

But the Home Office urged forces to carry on retaining the facial images, promising new laws would follow. At least 20 million mugshots are stored – a staggering one-third of the UK population.

Meanwhile, a “biometrics strategy” has been delayed for five years, prompting a watchdog’s warning that the number of retained images would rocket, breaching “individual privacy”.

Now Norman Lamb, the chairman of the Commons science and technology committee, has told The Independent that his committee is ready to step in and investigate.

Condemning the situation as “intolerable”, Mr Lamb said: “There are no real rules surrounding this.

“The police can store these facial images without any proper consideration of them, which raises fundamental and significant civil liberty issues about what they are retaining about us.

“It includes people who have not been charged with any crime, or people who have been exonerated.”

The Liberal Democrat MP said an additional worry was the disproportionate targeting of ethnic minorities, adding: “There are also concerns about bias – and also about the accuracy of identification.

“This is not to say the technology doesn’t have it place, or potential value, but it needs to be operated within a clear legal and regulatory framework.”

Mr Lamb said he would push for Baroness Williams, the Home Office minister responsible for biometrics, to be hauled before his committee, when it discusses the controversy on Tuesday.

If the minister failed to provide satisfactory answers – which she failed to do in a letter sent before Christmas, he said – a full inquiry by the committee would follow.

Concern has grown about the mugshots database as police have developed the ability to capture images using cameras in public places, as well as of people arrested or questioned.

Around 16 million mugshots are thought to be held on IT systems that can be searched using facial recognition software, allowing new images to be checked against those existing records. And a further four million, which are also stored, are not searchable using that software.

Police say officers use the technology to identify suspects, offenders and witnesses and to help with searching for unidentified suspects, such as those spotted on CCTV.

The practice provoked controversy at last year’s Notting Hill carnival, when police used facial recognition software to scan the faces of revellers, despite protests that it was unlawful and institutionally racist.

In 2012, the High Court ruled that retaining the images of people not convicted of any crime for six years, before police decided whether to delete them, was not proportionate.

Last year, the Home Office announced a review but said the police would still not have to reconsider retention until after six years – and after 10 years for more serious alleged offences.

The only response to the court ruling was that people would be able to apply to the police to have their images deleted at the end of any proceedings.

There would be a “presumption in favour of deletion”, but the police would be entitled to refuse such an application.

Professor Paul Wiles, the independent Biometrics Commissioner who warned the database was set to grow and grow, has suggested this would not survive a further legal challenge.

He pointed out that just 1,003 of the 896,209 people arrested in 2015-16 had applied to have their records deleted, under separate rules – and only 233 of those requests were accepted by the police.

Professor Giles warned of the danger of losing public confidence, saying last year: “The review leaves the governance and decision-making of this new process entirely in the hands of the police.”

Mr Lamb has also raised the alarm that the review, in the absence of a wider strategy, dealt only with image retention and not “uncertainty about how facial images are captured and used”.

In fact, Baroness Williams had stated the use of images is an “operational matter’ for the police, without any apparent guidance having been issued to forces.

Mr Lamb has demanded to know whether the strategy will consider the “proper and appropriate use” of images – as well as when it will be published. Baroness Williams has said only that it will appear sometime in 2018.

In contrast, many DNA and fingerprint records have been deleted under legislation brought in by the coalition government, which promised to “roll back the database state”.

Ministers have argued mugshots are “less intrusive” because people’s faces are on public display, but Professor Giles said: “I disagree with that assertion.

“In fact, for that reason, the use of facial images is more intrusive because image capture can be done using cameras in public places and searched against government databases without the subject being aware.

“Facial images are no longer only used solely for custody purpose, and image capture and facial searching capabilities have and are being used by the police in public places.”