Primary school children should be eligible for the DNA database if they exhibit behaviour indicating they may become criminals in later life, according to Britain's most senior police forensics expert.

Gary Pugh, director of forensic sciences at Scotland Yard and the new DNA spokesman for the Association of Chief Police Officers (Acpo), said a debate was needed on how far Britain should go in identifying potential offenders, given that some experts believe it is possible to identify future offending traits in children as young as five.

'If we have a primary means of identifying people before they offend, then in the long-term the benefits of targeting younger people are extremely large,' said Pugh. 'You could argue the younger the better. Criminologists say some people will grow out of crime; others won't. We have to find who are possibly going to be the biggest threat to society.'

Pugh admitted that the deeply controversial suggestion raised issues of parental consent, potential stigmatisation and the role of teachers in identifying future offenders, but said society needed an open, mature discussion on how best to tackle crime before it took place. There are currently 4.5 million genetic samples on the UK database - the largest in Europe - but police believe more are required to reduce crime further. 'The number of unsolved crimes says we are not sampling enough of the right people,' Pugh told The Observer. However, he said the notion of universal sampling - everyone being forced to give their genetic samples to the database - is currently prohibited by cost and logistics.

Civil liberty groups condemned his comments last night by likening them to an excerpt from a 'science fiction novel'. One teaching union warned that it was a step towards a 'police state'.

Pugh's call for the government to consider options such as placing primary school children who have not been arrested on the database is supported by elements of criminological theory. A well-established pattern of offending involves relatively trivial offences escalating to more serious crimes. Senior Scotland Yard criminologists are understood to be confident that techniques are able to identify future offenders.

A recent report from the think-tank Institute for Public Policy Research (IPPR) called for children to be targeted between the ages of five and 12 with cognitive behavioural therapy, parenting programmes and intensive support. Prevention should start young, it said, because prolific offenders typically began offending between the ages of 10 and 13. Julia Margo, author of the report, entitled 'Make me a Criminal', said: 'You can carry out a risk factor analysis where you look at the characteristics of an individual child aged five to seven and identify risk factors that make it more likely that they would become an offender.' However, she said that placing young children on a database risked stigmatising them by identifying them in a 'negative' way.

Shami Chakrabarti, director of the civil rights group Liberty, denounced any plan to target youngsters. 'Whichever bright spark at Acpo thought this one up should go back to the business of policing or the pastime of science fiction novels,' she said. 'The British public is highly respectful of the police and open even to eccentric debate, but playing politics with our innocent kids is a step too far.'

Chris Davis, of the National Primary Headteachers' Association, said most teachers and parents would find the suggestion an 'anathema' and potentially very dangerous. 'It could be seen as a step towards a police state,' he said. 'It is condemning them at a very young age to something they have not yet done. They may have the potential to do something, but we all have the potential to do things. To label children at that stage and put them on a register is going too far.'

Davis admitted that most teachers could identify children who 'had the potential to have a more challenging adult life', but said it was the job of teachers to support them.

Pugh, though, believes that measures to identify criminals early would save the economy huge sums - violent crime alone costs the UK £13bn a year - and significantly reduce the number of offences committed. However, he said the British public needed to move away from regarding anyone on the DNA database as a criminal and accepted it was an emotional issue.

'Fingerprints, somehow, are far less contentious,' he said. 'We have children giving their fingerprints when they are borrowing books from a library.'

Last week it emerged that the number of 10 to 18-year-olds placed on the DNA database after being arrested will have reached around 1.5 million this time next year. Since 2004 police have had the power to take DNA samples from anyone over the age of 10 who is arrested, regardless of whether they are later charged, convicted, or found to be innocent.

Concern over the issue of civil liberties will be further amplified by news yesterday that commuters using Oyster smart cards could have their movements around cities secretly monitored under new counter-terrorism powers being sought by the security services.