Building more prisons will result in a huge rise in the proportion of criminals who reoffend, a criminology expert has said.
A study by Dr Carol Hedderman, a former senior Home Office researcher, has shown a direct relationship between the expansion of the prison population and the growth in the percentage of prisoners reconvicted within two years of leaving jail.
Britain's prison population has increased by more than a third in the past decade. At the same time, the percentage of prisoners committing offences within two years of leaving has surged from just over half to almost two-thirds.
In 1993, when there were fewer than 45,000 prisoners, 53 per cent were being reconvicted within two years. In 2004, 65 per cent of those leaving prison were reconvicted.
The Government's plans for prison-building are on a larger scale than the construction under way for the 2012 Olympics. But this research suggests the proposed 5,000-place Titan prisons will be counter-productive. "Every time we build a new Titan prison, we'll see thousands more people offending again," Dr Hedderman, professor of criminology at the University of Leicester, said.
If the number of people put behind bars continues to expand, the proportion of those who end up committing further offences will also grow, she added. "If current trends continue, in another 10 years we can expect to see the numbers of prisoners reoffending [within two years of release] rise to three-quarters."
Dr Hedderman believes that the reason prison numbers are rising is that people are being put behind bars for more minor offences. According to her research, this trend has led to the vast increase in reoffending, because prisoners in jail for lesser crimes serve shorter sentences.
She argues that these brief spells in prison are long enough to disrupt the lives of offenders and put them in contact with more serious criminals, but too short to allow them to benefit from the education or training available in jail.
"The people who used to be fined are now getting community penalties, and the people who used to get community penalties are now going for short prison sentences – it's all shifted along," she said.
"Most boys mature out of offending, but if you don't wait for them to mature out of it you stigmatise them with a criminal record and then they don't stand much chance of getting back into society. Sometimes on longer sentences people can get something productive from it, but if you send someone to prison for three months they won't be there long enough to get any serious education."
The Ministry of Justice says the reconviction rate is dropping, but this is because they use "modelled" reconviction rates, which adjust the figures according to how they compare with what the Government predicted the rate would be. Dr Hedderman believes these are no longer appropriate to use now that the types of offenders in jail have changed. Her research is based on the "raw" reconviction figures.
Enver Solomon, deputy director of the Centre for Crime and Justice Studies at King's College London, who commissioned the research, said: "It's clear that incarceration causes immense social and economic damage to individuals and their families, and as a result it's a crime generator.
"People go to prison and go on to commit many further offences. Prison will never be an effective crime-control tool because the evidence clearly demonstrates that it actively creates or compounds the factors that contribute to offending."