Genetic information taken from nearly 1.1 million children is now stored on the national DNA database, official figures show, and campaigners believe that as many as half of them have no criminal convictions.

The figure fuels the row about retention of personal information on the DNA register and on the police national computer for years after it ceases to be relevant.

The figures, revealed in a parliamentary answer to the Liberal Democrats, show that 1.09 million DNA profiles of people aged under 18 were held on the database with 337,000under 16.

The Met police has added by far the largest number of profiles to the register, 117,000 boys and 33,000 girls. The second biggest number is in the West Midlands force area, 49,000 and 17,000 respectively.

The Lib Dems' home affairs spokesman, Chris Huhne, said: "We already know that guilt and innocence are of no concern to ministers, but clearly neither is the negative effect the database has on children.

"It is unacceptable to keep the DNA of children on record in perpetuity for the most minor of offences. Unless convicted of a sexual or violent offence, under-16s should not have their DNA stored on the database."

Around 570,000 child profiles have been added in the last five years. Campaigners blame changes in police tactics to meet targets for the rise in the number of children on the register.

Terri Dowty, of Action on Rights for Children, said: "Many children get arrested, have their DNA taken and there is no further action against them or they get a reprimand or final warning. We are collecting massive amounts of data on children, including how likely they are to be criminals, and it runs the risk that we will prejudge them."

The National Policing Improvement Agency (NPIA), the body in charge of the database, said that 88% of children were charged, convicted, or received a final warning. But it could not say how many of those charged were acquitted or what proportion received a final warning, which does not count as a criminal conviction.

"We believe that the government underestimates the number of innocent children on the database," said Helen Wallace, the director of GeneWatch, a campaign group which has calculated that about half of children added to the database are innocent. "There has been a very large increase in the number of children arrested in past few years and this has been driven by the government arrest targets."

Britain's DNA database is proportionately the biggest in the world and includes the profiles of more than 7% of the population, according to Home Office figures. Almost everyone arrested for a recordable offence is required to provide a DNA sample. Whether or not criminal proceedings follow, DNA records stay on file until the person reaches their 100th birthday.

Police insist the database is an invaluable tool in fighting crime. However, a European court of human rights ruling last December found the government was violating the rights of two innocent UK citizens whose DNA details continue to be held.

Peter Mahy, a solicitor who represented one of the men, said: "We have probably had a thousand calls from people in similar circumstances since the ruling in December, and many thousands since we started acting for these clients five years ago.

"The fact that it got to the House of Lords and got chucked out then went to Europe and all 17 judges ruled in our favour shows the massive gulf between the British authorities and other countries."

Following the European decision the home secretary, Jacqui Smith, promised to consult on bringing greater flexibility and fairness to the system, and raised the prospect that some people's details could be removed over time.

Peter Neyroud, the NPIA chief executive, told a Lords committee last year that the database "continued to grow in significance as a national intelligence resource".

In a separate development, five police forces are appealing against an Information Tribunal decision last July that they must destroy decades-old criminal records because they are no longer relevant. People whose data was stored in criminal records complained after their history showed up in Criminal Records Bureau checks when they applied for jobs.

The forces are Humberside, Northumbria, Staffordshire, Greater Manchester and West Midlands.

'I am blackmarked for life'

John Webb, 47, from Hull, runs a paragliding business and was in the army for 20 years. When he applied for clearance to work with children, a minor conviction surfaced, dating back to a fairground trip when he was 16. "One of my friends had some metal discs the size of 1p or 10p pieces, and he put them into one of the slot machines which allegedly short-circuited," he said. The friends were taken to a police station, and he admitted attempted theft and minor criminal damage to the machine. He says police said his details would only be kept until he was 18.

"I felt surprise, shock, horror and disgust at my being portrayed as convicted of attempted theft and criminal damage," Webb said of the disclosure. "Although I accept what happened in the incident was wrong, I consider that by today's standards what I did would be considered more of a juvenile prank.

"I do not have a problem with the police holding the information. It is how it has been used. The conviction has nothing to do with children and ... 31 years later it is still holding me back. I could not emigrate to Canada, for example. I am pretty sure my information has now been stepped down, meaning it won't appear on a CRB check again, but it is too late. I am blackmarked for life."

• In 1984, a 16-year-old, who has not been identified, was fined £15 for stealing a 99p packet of meat from Marks & Spencer. Twenty-two years later and working as a care assistant, the conviction came up in a CRB check. "I told my manager that I had completely forgotten about the incident, which I had. I was left with the impression that I could well lose my job," he said.

He kept the job but his position was downgraded the following year and his salary cut. He blames the check. "I am devastated that it has been disclosed to my employer, as I have no idea who may now know about this matter."

• Kylie Smith was 14 when she was attacked by a girl she had known at school. In defending herself, she pushed the girl to the ground. Three days later, she was arrested. "I was accused of kicking her, which I denied because I had not done it, but the sergeant said if I did not admit to kicking I would have to go to court. However, if I did admit it I would be given a reprimand and be allowed to go home."

Four years later, she began working as a social care assistant, but a Criminal Records Bureau check led to her employment being terminated. She took the complaint to the information commissioner, who ordered the caution to be removed from the register.

• John Cann intervened after he saw a drunken man trying to smash a woman's car windscreen and drag her out. The man turned on Cann, of Twickenham, west London, who laid him out with one punch. Despite witness testimony, police arrested Cann. It was only after MP involvement that his DNA sample was removed from the database.