DNA from nearly 4,000 children, including a two year-old, was taken by Thames Valley Police over two years, figures have revealed.

The force which polices Bucks, Berks and Oxfordshire, took samples from a seven-year-old and a two-year-old, according to data obtained by the charity The Howard League for Penal Reform.

The amount of children whose DNA was kept is excessive, its Chief Executive said.

New research, which the organisation carried out, found that officers took swabs from 3,947 youngsters below the age of 17 in 2010 and 2011 in the Thames Valley area.

Many of the children required to give a sample will not have been charged with a criminal offence. Under current rules, police can retain indefinitely the DNA of anyone they arrest for a recordable offence. A new law, imposing tighter restrictions on DNA retention, is expected to come into force later this year.

Frances Crook, Chief Executive of the Howard League for Penal Reform, said: "When public money is tight and police forces are shrinking, it is disappointing to see valuable crime-fighting resources being wasted on taking DNA samples from thousands of innocent children while serious offences go undetected.

"Children who get into trouble with the police are usually just up to mischief. Treating so many like hardened criminals by taking their DNA seems excessive.

"We welcome the government’s decision to stop storing innocent people’s DNA indefinitely, but it remains unclear how this will affect the number of children having their DNA taken needlessly."

The Bucks Free Press understands the two samples taken from the children aged seven and two, by TVP, were not suspects, and both were taken with parental consent.

Thames Valley Police said in a statement: "DNA may be taken from children in a number of circumstances with the intention of preventing or detecting crime. "These may be when a child has been a victim of crime, when police would take DNA to confirm an incident took place and check whether it can be linked to a perpetrator.

"Others will be as part of criminal investigation where a child is the suspect. "DNA samples are also taken to conduct criminal paternity tests as part of sexual offence investigations. The taking and retention of DNA from people of all ages is set out clearly under law."

Other cases highlighted by the charity included Avon and Somerset Police, which took a sample from a five-year-old and Gloucestershire Police, which took DNA from a baby who was younger than 12 months.

About 30 per cent of the child DNA samples taken by police come from girls. The total number of children in England and Wales who had DNA samples taken by police was 69,796 in 2010 and 53,973 in 2011.

Wycombe MP Steve Baker sat on the public bill committee for the Protection of Freedoms Act which tightened the law in this area.

He said: "I feel strongly that biometric information ought not to be collected and retained routinely in relation to those not under investigation nor convicted of an offence.

"The DNA of innocent people ought not to be collected except to eliminate them from inquiries.

"I felt that the new Act could have gone further and I proposed a number of amendments which were not accepted by the Government."

He added there was always balance to be struck between security and liberty.