One in three criminals are prolific offenders with more than 15 convictions Ministry of Justice figures show worrying rise in hardened criminals Convictions for serious and more minor offences see rise Average prison sentence length jumps dramatically in 10 years Prison expert says public is at risk from repeat offenders Hardened: Ministry of Justice figures show a worrying rise in repeat offenders. The number of criminals with 15 or more previous convictions or cautions is now one in three. The number of criminals with 15 or more previous convictions or cautions has steadily risen in the last decade to one in three, figures showed today. A third of criminals convicted of serious offences last year were prolific offenders, compared with one in five in 2002, the Ministry of Justice said. The number of criminals convicted in magistrates' courts with 15 or more earlier convictions or cautions has also risen in the same period from one in 10 to one in five. A prison expert has called the figures 'shameful' and claims these repeat offender put the public at risk. The figures also revealed a fall in the number of serious offenders with 15 or more previous convictions or cautions given a community sentence, down one in five. Meanwhile, the average custodial sentence length was 14.9 months, up from just 2.5 months in 2002. The figures showed that 1.86 million people were either given a caution or other out-of-court disposal or taken to court in the year to September, down 8.4 per cent from 2.03 million individuals in the previous year. Police cautions fell 12.5 per cent to 205,700 in the year to September, while use of on-the-spot fines for public disorder fell 15.8 per cent to 109,600. Commenting on the figures, Frances Crook, chief executive of the Howard League for Penal Reform, said: 'This is a complicated picture. We welcome the fact that there are fewer first-time entrants into the criminal justice system than in previous years. Out of court warnings, penalties and cautions, September 2002 to September 2012 Offenders receiving an indeterminate custodial sentence and average custodial sentence length for all offenders; September 2002 to September 2012 However, these statistics lay bare the shameful record of failure in our justice system - in particular, the failure of short-term prison sentences, often handed out for non-violent and low-level crimes. Revolving-door prisons create a cycle of homelessness, drug addiction and poverty, with people often going on to commit ever more serious crimes. A year behind bars, as these statistics show, can easily become a life sentence with no way out. Frances Crook, penal reformer There were 187,700 first-time offenders in the year, a decrease of 12.8 per cent on the year and a 43.6 per cent fall when compared with the year to September 2007. Of the 1.23 million offenders sentenced during the 12 months ending September 2012, 97,500 were sentenced to immediate custody, a decrease of 4.7 per cent. Peter Cuthbertson, director of campaigners the Centre for Crime Prevention said: 'The latest figures confirm a growing trend for some of the most serious, repeat offenders avoiding prison, putting the public at risk. 'Community sentences shouldn't be used for hardened criminals with 15 previous convictions.' Justice Minister Jeremy Wright said: 'Crime is falling and the use of cautions is now at its lowest level for over a decade. A greater proportion of convicted criminals are going to prison and their sentences are longer than ever before. However, reoffending rates have barely changed in a decade and we cannot go on doing the same thing and expecting a different result. That is why we are pressing ahead with major reforms that will tackle this problem. Caged: Average sentence lengths have jumped sharply in the last ten years