DNA profiles and fingerprints of almost 8,000 individuals have been stored on a police counter-terrorism database, it has been disclosed.
Records relating to 7,800 people were logged as of October last year, a report by an official watchdog said.
The archive - which is separate from the larger national DNA database - includes biometric details of thousands of individuals who have not been convicted.
It was also revealed that at least 45 records will have to be deleted, even though authorities may have sought to hold them on national security grounds.
A report from Biometrics Commissioner Alastair MacGregor QC said that in October 2013 the DNA profiles and/or fingerprints of some 6,500 identified individuals were being held by police forces on the national counter-terrorism database.
Two years later the number stood at 7,800.
It is believed to be the first indication of the size of the database to be made public. The total is higher than previous indications of the number of terror suspects in the UK.
Of the individuals whose biometric records were being held by police on counter-terrorism databases, 4,350 - or around 55% - had never been convicted of a "recordable" offence. This is generally a crime which can attract a prison sentence.
Previously DNA profiles and fingerprints could be retained indefinitely regardless of whether someone had been convicted or not.
Under the current regime rolled out in 2013 this is permitted in circumstances when someone is convicted of a recordable offence, but in most other circumstances the details should be deleted at the conclusion of an investigation or proceeding.
However the rules allow for the extended retention of material taken from an individual who has not been convicted of a recordable offence when a senior officer makes a national security determination (NSD). These allow biometrics to be kept for up to two years and can be renewed.
By October the cases of 1,900 individuals who had not been convicted but whose records were being retained on the counter-terrorism databases had been reviewed, with NSD applications submitted for around 11%.
It was also disclosed that records for which NSDs may have been sought must be erased.
Mr MacGregor's report said: "I understand that by 31 October 2015 handling and other delays had led to a situation in which the statutory retention periods in respect of the biometric records of at least some 450 individuals had expired before NSDs could be or had been made in relation to them.
"Although it seems unlikely that NSDs would have been applied for and made in relation to more than a small proportion of those records, I also understand that in about 10% of those cases it is possible that NSDs would have been applied for.
"Indeed, in at least three of those cases such applications had in fact been made and approved."
The commissioner added that he had been assured that "urgent steps" are being taken to "procure the speedy deletion" of material that has remained on counter-terrorism databases "beyond its lawful retention date".
A spokeswoman for the National Police Chiefs' Council said: "The fingerprint and DNA data of a small number of individuals who potentially pose a threat to national security have been deleted from biometric databases as the retention period expired before a national security determination (NSD) could be submitted for approval.
"The identity of these individuals is known and the risks they potentially pose are being managed in conjunction with partner agencies.
"Comprehensive measures have been put in place to prevent the loss of further biometric data from individuals of concern before an NSD is applied for."
Daniel Nesbitt, research director of Big Brother Watch, said the report "raises a number of important concerns that will just pile more pressure on the Home Office to sort out its approach to biometric technology".