The youngsters — aged between 10 and 18 — have never been cautioned, charged or convicted of any offence, and in some cases may simply have witnessed a crime.

The number of DNA profiles taken from youngsters emerged during an investigation by an MP into complaints that a constituent’s son had been profiled after being wrongly arrested.

Grant Shapps, the Conservative MP for Welwyn Hatfield, has now obtained an assurance from Frank Whiteley, the Hertfordshire chief constable, that the teenager’s details will be removed from the database.

Shapps is campaigning to have all records of youngsters who are not guilty of any wrongdoing to be erased from the database.

“There are certainly cases of kids picked up and never charged or even cautioned for anything. So it is hard to see why the details should be kept on the database. They are innocent children, basically,” Shapps said.

Details of 7% of the population are expected to be held on the database by April 2008.

The boom in the number of records held follows a change in the law in 2001 which allowed samples to be taken from people who have been acquitted of a crime, or arrested for a recordable offence but not charged.

In some cases samples have been stored from witnesses, or even from the victims of assaults or robberies.

Yesterday Professor Sir Alec Jeffreys, the British pioneer of DNA profiling, was also reported to be concerned about the size of the database.

“We are facing a potentially serious threat to civil liberties,” Jeffreys said.

The government has defended its policy of storing children’s DNA profiles, arguing that almost a quarter of all arrests are of children and teenagers.

Andy Burnham, a Home Office minister, told the BBC Radio 4 Today programme that the DNA database was not a criminal record.

“The database simply reflects operational policing practice in Britain,” he said.

“We may not feel comfortable with this fact, but under-18s represent about 23% of arrests in Britain.”

Among those campaigning to have a child’s DNA removed from the database is Helen Sabonjian, a teacher from Harrow, west London.

Her teenage son, Mark, was among a group who witnessed a robbery in December 2004 but was arrested on suspicion of the crime, despite being innocent.

“It was a very horrific ordeal . . . but the fact that his details were retained for ever was the icing on the cake,” she said.

“It’s not right. It should not happen. Why should my son be on the database for doing nothing?” The Association of Chief Police Officers said yesterday that taking samples from people who have not been convicted has produced more than 3,000 DNA matches with unsolved crimes, including murders and rapes.

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