Nick Clegg: Do you want to create crime, or cut it?

Prison should turn lives around, not reinforce patterns of criminal behaviour

The public is being duped. The Government and the Conservatives are deluding themselves. We are sleepwalking to precisely the wrong conclusion about the prison overcrowding crisis. The difficult truth is that we cannot build our way out of the overcrowding crisis. Demand will continue to outstrip supply. It's like building new lanes to the M25; they just keep filling up.

The Government and David Cameron pretend that if we only add another few thousand cells, we will somehow have a prison system that works. But Britain already locks up more of its citizens than any other country in Western Europe.

Reoffending rates are at record highs, because we use prisons simply to warehouse people for a few months or years. They are let out unreformed and soon reappear in front of the courts. Ninety two per cent of young men sentenced to prison for three months or less now go on to reoffend.

Home Office studies have shown that to cut crime by a single percentage point, we would need to increase the prison population by 15 per cent - that's another 12,000 people locked away at a cost of £500m a year.

Those who advocate ever more prisons never answer the question: "Where do we stop?" Twenty thousand prison places have been built in the past decade, and still the prisons are full. Should we double numbers? Treble them? Should we just permanently lock up all 1.5 million people who've done time, at a cost of about £50bn a year?

The answer is no. The only way to solve the crisis is to take concerted action to cut reoffending, and to develop smarter ways to punish and rehabilitate offenders. Instead of prisons we should expand specialised secure facilities where the problems, notably mental health problems, that drive some people to crime can be tackled.

Low-level offenders should be punished and rehabilitated outside prison, with sentences of visible public service far more demanding than a few weeks lounging in a prison cell. Those who remain in prison should work, or undergo comprehensive training and education. Children should only ever be put in prison as a last resort.

And the antique prison estate, where wings declared unfit for human habitation are being brought back into use, should be sold off wherever possible and replaced with modern buildings where offenders can be turned away from a life of crime. City centre prisons - like Brixton and Pentonville - occupy prime real estate but are simply not fit for purpose.

Liberal Democrats would divert the £1.5bn John Reid has earmarked for more prisons to expanding the provision of secure and semi-secure mental health and drug treatment facilities for offenders. About half of prisoners have some form of mental health problem, and one in 10 are estimated to be "functionally psychotic". But there are simply not enough mental health beds: special hospitals offer only 1,150 and court diversion schemes that recommend treatment for offenders are held back by the lack of beds.

As for drugs, three quarters of male prisoners admit taking illegal drugs in the 12 months before imprisonment, and 55 per cent said their offence was related to their drug addiction. Residential treatment should be offered more widely as an alternative to custody for low-tariff offenders. Even sending one in 10 offenders to residential drug treatment instead of prison would save about £40m a year.

Prison will remain a vital part of our criminal justice system, but it should be used to turn lives around, not reinforce patterns of criminal behaviour.

Work and training should be at the core of every prison regime. Offenders often go back to crime because they have little alternative, with few skills or qualifications: half of all prisoners are at or below the level expected of an 11-year-old in reading. Education programmes are hampered by overcrowding.

Liberal Democrats would triple the number of prisoners doing paid work, and make education and training compulsory. Prisonerswould be paid at market rates, and be liable for taxes, National Insurance and child support in full. They would also make a contribution to a victim compensation fund.

The prison crisis has revealed a stark clash of visions of the criminal justice system: the narrow, headline-grabbing vision of mass incarceration, in which an overburdened prison system is pushing thousands of individuals towards a life of repeat crime; and a liberal vision, which believes in changing the behaviour of offenders. The former creates crime, the latter cuts crime. A liberal vision would deliver greater public safety.

The writer is the Liberal Democrat spokesman on Home Affairs