Cautions have overtaken convictions as punishment for violent crimes for the first time, a report reveals today.

The number of assault cases where police allow offenders to escape punishment has more than trebled in five years to more than 118,000  -  including a near-doubling of the most serious violent attacks.

The rapid expansion of 'instant justice' under Labour has seen a dramatic rise in the use of formal warnings, cautions and on-the-spot fines by police as an alternative to pressing criminal charges.

The detailed study by Professor Rod Morgan, former chairman of the Youth Justice Board, warns the trend could be diverting serious offenders  -  who would previously have been dealt with in court  -  towards lesser punishments.

More than 118,000 violent thugs have got off with cautions under Labour's instant justice policy. Posed by models

Prof Morgan's report, published by the Centre for Crime and Justice Studies, King's College London, exposes the full extent of the growth in instant justice.

Police and prosecutors have embraced the policy, partly in response to controversial Whitehall targets which give equal credit for cautioning a child for a trivial disturbance as for catching a murderer.

Cautions handed out for 'more serious violence against the person'  -  assaults where victims are badly hurt  -  rose by 92 per cent to 916 between 2001 and 2006. It means nearly a quarter were given cautions, up from 14 per cent.

For less serious violence, cautions leapt from 19,090 to 56,357.

While convictions also rose, from 32,390 to 38,622, the proportion of offenders charged and sent to court plunged from 63 per cent to just 41 per cent.

The increase was repeated for common assault where cautions more than trebled to 60,938.

But the trend is not restricted to violent crime. In 2000 almost twothirds of those caught shoplifting  -  some 77,000  -  were charged and appeared before magistrates.

But by 2006 that had slumped to 41 per cent, or 58,000 offenders, while 32 per cent were cautioned and 27 per cent given fixed penalty fines of £80.

Penalty Notice Disorder fines were introduced in 2003 to deal with minor disorder, but were extended to cover shoplifting up to a value of £200, and criminal damage up to £500.

The findings follow years of efforts by Labour to 're-balance' the criminal justice system, aiming to deal with more offenders without swamping the courts with less serious cases.

While the total number of offences brought to justice grew from just over a million in 1999 to 1.4million in 2007, virtually all the increase was accounted for by the rise in cautions, fines and formal warnings.

Professor Morgan's report suggests greater use of these powers by police is 'dragging into the criminal justice system offenders and offending behaviour that would not previously have been criminalised'  -  particularly 'marginal' offences by young people.

In the past such cases were dealt with 'possibly quite effectively' by teachers, neighbours and pub landlords rather than the courts.

Shadow Home Secretary Dominic Grieve said: 'Labour's ad hoc and distorted approach has created the worst of both worlds.

'Not only are serious offenders escaping real justice due to the reliance on spot fines but, as this report shows, many people who should be dealt with informally are being criminalised.'

He added: 'The public are sick and tired of this Government pursuing easy targets, instead of going after the real criminals.'

A Department of Justice spokesman said: 'The law-abiding majority want to see crimes dealt with effectively and fixed penalty notices and cautions are part of this process.

'They allow police to deal swiftly with low-level offending, freeing them up to spend more time on frontline duties and more time investigating violent, dangerous and serious offences. They also free up court time for more serious cases.'