Officers are targeting children as young as 10 with the aim of placing their DNA profiles on the national database to improve their chances of solving crimes, it is claimed.
The alleged practice is also described as part of a “long-term crime prevention strategy” to dissuade youths from committing offences in the future.
Civil liberty campaigners have condemned the tactic of as “diabolical” and said it showed contempt for children’s freedom.
A Metropolitan Police officer made the claims after figures were released showing that 386 under-18s had their DNA taken and stored by police last year in Camden, north London.
The officer said: “Have we got targets for young people who have not been arrested yet? The answer is yes. But we are not just waiting outside schools to pick them up, we are acting on intelligence.
“It is part of a long-term crime prevention strategy. If you know you have had your DNA taken and it is on a database then you will think twice about committing burglary for a living.
“We are often told that we have just one chance to get that DNA sample and if we miss it then that might mean a rape or a murder goes unsolved in the future.”
Last month the Home Office drew up plans to amend the DNA database after the European Court of Human Rights ruled that a blanket policy of retaining profiles of innocent people indefinitely was illegal.
However, adults and children arrested, but not convicted, of terrorism or serious sexual or violent offences will still have their profiles held for 12 years before they are deleted.
Children not convicted of any other offence will have profiles erased after six years or when they reach 18, whichever is sooner.
The Home Office announced last year that the DNA of children under 10 will not be retained.
Shami Chakrabarti, director of the human rights group Liberty, said: “This is diabolical and proof positive that Liberty’s fears are being realised.
“The current law has created an incentive for the abuse of police power so that youngsters are being targeted purely for the purpose of stockpiling their DNA for the future.
“We hope that dealing with this outrage will be high on the list of priorities for any new Home Secretary.
“Politicians can no longer demand due process for themselves whilst showing such contempt for the freedoms of others.”
Figures obtained via a Freedom of Information request show that a further 139 youths arrested in the Camden area have had their DNA profiles added to the database this year.
Lib Dem parliamentary candidate for Holborn and St Pancras, Jo Shaw, who applied for the data, said: “The Met and the Home Office have some serious explaining to do if this is the case.
“Innocent children should not have their DNA profiles kept for years.”
There are an estimated 5.3 million profiles on the DNA database – accounting for about one in 10 people – making it the largest of its kind in the world.
However 850,000 are of people who were never convicted of any crime. Murray Wardrop