By Alexander J Martin, technology reporter
Huge investment will be needed to upgrade police IT systems to ensure the use of facial recognition technology is legal, Sky News has learnt.
Metropolitan Police has run 10 trials of live facial recognition technology which scanned the faces of the public against a database of people of interest.
But the force's back-end IT systems are not capable of letting officers check whether the images on the database are being held legally.
Johanna Morley, the Met's senior technologist, told Sky News that this governance of the watch-list was a matter of concern.
This comparison database is currently created manually and in accordance with a High Court ruling in 2012 which requires the police to only hold the images of people who are legitimate subjects of interest.
However, in two trials run by the Met the comparison database accidentally held the images of people who did not meet the criteria due to having been already dealt with.
Speaking to a policing ethics panel event, Ms Morley said this was due to the Met's "back-end technology systems" which are incapable of automatically synchronising with the facial recognition systems.
More from London
The High Court ruling in 2012 told the police that it was unlawful for them to hold innocent people's facial images on their systems.
A government response defended police when it came to the poor quality of their IT systems which made it impossible to automatically delete those images, however it did not change the ruling.