Labour's attempts to restore public confidence in the criminal justice system have led to a huge rise in the criminalisation of people for minor offences, according to a key government adviser.

Professor Rod Morgan, a former chief inspector of probation and the ex-chair of the Youth Justice Board, warns in a report released tomorrow that more people are ending up with criminal records owing to the increasing use of cautions and fixed-penalty notices handed out by the police. His comments are likely to strike a chord with a growing number of parents concerned that their children are receiving criminal records and having their personal details recorded on the DNA database even for minor offences.

Morgan also suggests that, conversely, an increasing number of people convicted of violent offences may be receiving cautions rather than ending up before the courts. He says that the expansion of 'summary justice' - penalties that do not need to be handed down by the courts - needed to be 'more incisively scrutinised to ensure that justice is being meted out fairly and effectively', adding: 'We cannot be wholly confident that this is the case.'

The increased use of summary justice was hailed by Labour as a way of boosting public confidence in the law. The idea, according to Lord Falconer, the then Lord Chancellor who heavily promoted its use, was 'to connect the instance of crime much more quickly and directly with the consequences of crime'.

But there are concerns that its widespread use is backfiring. The number of cautions has risen from 900,000 in 2002 to 1.4 million in 2006, the most recent figures available. Over the same period, the number of penalty notices for disorder has soared from 1,000 to 513,000.

Such sanctions have in many cases replaced informal legal remedies such as a 'ticking off' from the local policeman. Morgan warns there is a risk that people 'will be criminalised where both common sense and the public interest suggest that informal control systems and informal sanctions would better apply'.

His decision to speak will dismay the Ministry of Justice. Morgan sits on a government criminal justice advisory board and his long record as a civil servant suggests his views will gain wide attention.

His report 'Summary justice: Fast but Fair?', published by the Centre for Crime and Justice Studies, also questions whether the trend towards handing out cautions and penalty notices might have resulted in some serious offenders receiving lighter sentences than if they had ended up in court.

Between 2001 and 2006 there has been a 92 per cent increase in the number of cautions handed down for serious violence against the person and a 267 per cent rise in cautions for common assault. The trend has resulted in an 'accountability deficit', according to Morgan, who points to significant regional variations in the use of penalties and cautions. In Dyfed Powys, for example, 61 per cent of indictable offences result in a caution, compared with a low of 21 per cent in Merseyside.

Richard Garside, director of the Centre for Crime and Justice Studies, said Morgan's report raised 'important questions about the consequences of government policies to divert minor offences from the courts'.

A Ministry of Justice spokesman said: 'Fixed penalty notices and cautions enable police to deal swiftly with low-level offending, freeing them to spend more time on frontline duties and more time investigating violent, dangerous or sexual offences, as well as freeing court time for more serious offences.'