Youths with no criminal past are being arrested so their DNA can be stored on a database, according to the Metro.
In the London borough of Camden, 386 under 18s had their DNA put on record in 2008 and 169 so far this year, a freedom of information request by Lib Dem parliarmentary candidate Jo Shaw has revealed.
Privacy campaigners were outraged when government announced plans last month to keep DNA information on innocent people for up to 12 years.
Home Office guidelines currently allow the police to obtain DNA from persons of any age who are arrested for a recordable offence, ranging from drug offences to murder.
The modified plans will see thousands of innocent people kept for six years, with the time limit extended for those who were arrested for serious crimes.
A senior Met officer said anonymously that the Camden arrests were part of a long term crime prevention strategy and that youths were being targeted in case they commit future crimes, according to the Metro.
However, the Met Police has strongly denied that there is a crime prevention strategy in Camden for taking DNA and that teenagers are arrested purely to obtain samples.
"Whilst any DNA samples obtained following arrest can lead to more serious crimes being solved, we do not actively seek to obtain DNA for this purpose," a spokesman said.
Police Officers operate within a legislative framework, he said, which enables them to effect arrests based on individual discretion that targets offenders, crime and criminality.
"The taking and retention of DNA is strictly governed by Home Office guidelines and adhered to by Camden Police," the spokesman said.