Police are arresting people just so they can take their DNA and boost numbers on the national database, the Government's own watchdog has warned.
Officers will arrest individuals for "everything" because they then have to power to take DNA samples, even if they wouldn't have been detained under other circumstances.
The Human Genetics Commission (HGC) warned the alarming practice, which was revealed by a retired senior police officer, was creating a "spiral of suspicion" over the DNA database.
In a major review of the system, it said police should no longer be allowed to automatically take DNA samples for everyone they arrest and called for new rules on when it was right to do so.
It suggested the growth in the programme, which is the largest of its kind in the world, stemmed from a pledge in 2000 by Tony Blair, the then Prime Minister, to have the DNA of every criminal within three years.
The Commission, an independent Government advisory body, also questioned the effectiveness of the database in helping to solve crimes and called for a detailed examination of its success.
A public debate and proper scrutiny of the system was needed as there was "very little concrete evidence" as to how useful the database was in investigating crime.
The report will fuel concerns over the growth of the surveillance state and the erosion of privacy.
Under the current rules, police can demand a DNA samples from anyone they arrest for a recordable offence.
In written submission to the HGC's review, a retired senior police officer, said: "It is now the norm to arrest offenders for everything if there is a power to do so.
"It is apparently understood by serving police officers that one of the reasons, if not the reason, for the change in practice is so that the DNA of the offender can be obtained: samples can be obtained after arrest but not if there is a report for summons.
"It matters not, of course, whether the arrest leads to no action, a caution or a charge, because the DNA is kept on the database anyway."
There are more than five million profiles on the DNA database, including up to one million innocent people who were never charged or convicted with an offence.
Professor Jonathan Montgomery, HGC chairman, said it had suffered from "function creep" over the years, transforming it from a database of offenders to a database of suspects.
"It's now become pretty much routine to take DNA samples on arrest," he said.
"So large numbers of people on the DNA database will be there not because they have been convicted, but because they've been arrested.
"Indeed, there was some evidence that we received, although it's hard for us to test, that occasionally people are arrested in order to retain the DNA information even though they might not have been arrested in other circumstances."
He warned it would create a "spiral of suspicion" and that it would be of "very great concern" if such practices were widespread.
Prof Montgomery added that more detailed research is required to evaluate how useful the database is in helping to solve crimes, describing current evidence as "flimsy".
He accused politicians of using single case studies where the database has secured a conviction instead of carrying out a rigorous evaluation of its scale and function.
"We have to strike a proper balance between identifying offenders and protecting privacy, including that of innocent people – we should not compromise that privacy without good reason," he said.
Over the past two years, more than 1.17 million profiles have been added to the database, according to the National Policing Improvement Agency, but the number of DNA-related detections fell from a peak of 41,148 in 2006-07 to 31,915 in 2008-09.
Chris Huhne, the Liberal Democrat home affairs spokesman, said: "The Government’s cavalier attitude towards DNA retention has put us in the ridiculous situation where people are being arrested just to have their DNA harvested."
James Brokenshire, the shadow home affairs minister, said: "Under Labour's surveillance state everyone is treated as a potential suspect."
The HGC report, Nothing to hide, nothing to fear?, also warned current policies have a "disproportionate effect" on different age and ethnic groups and worries about some being stigmatised.
Young black men are "very highly over-represented" the report says, with more than three quarters of those aged 18-35 on the database.
New proposals within the Crime and Security Bill – published last week – will for the first time put a time limit, in most cases six years, on how long profiles are stored when the alleged offender is either not charged or later cleared. But there are currently no plans to diminish police powers to take samples on arrest.
A Home Office spokeswoman said: "Research shows no clear link between the level of offence for which an individual is arrested and the seriousness of any subsequent offence with which they may be associated.
"DNA samples are taken on arrest for recordable offences carrying a prison sentence.
"The Government is clear that this is the right threshold for taking and retaining DNA."
By Tom Whitehead, Home Affairs Editor
24 Nov 2009
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Police arrest so they can boost DNA database, warns watchdog