Sadiq Khan is right to highlight the "growing crisis in our prison system" ('Ken Clarke needs to wake up to the looming crisis in our prison system'). Since the August riots, the prison population in England and Wales (already one of the highest in Western Europe) has been on an upward trajectory, with new record highs reached in each of the past four weeks. However, his criticism of concrete plans to reduce the prison population as "artificial measures", aimed solely and cynically at "cutting costs", is misplaced.

One of the problems Mr Khan identifies within the prison system, which he correctly links to high reoffending rates, is that of prisoners "idling" in their cells, with limited access to education and training, and to support including mental health care and drug and alcohol treatment. This is the result of a bloated prison estate, unable to do anything meaningful with those it holds because of a lack of time, space and resources. The Chief Inspector of Prisons has neatly pinpointed the effects of prison overcrowding in his recently published annual report: "It is not that terrible things are done to prisoners; it is that for too many, nothing much happens at all."

Addressing this problem, Sadiq Khan suggests that continuing to pour money into the prison estate is the answer - that we can build our way out of the overcrowding crisis. History, however, suggests otherwise. Between 2003-4 and 2008-9, for instance, expenditure on prisons increased by nearly 40% in real terms, reaching just under £4 billion a year. And yet, in spite of the prison building programme funded by this increased spending, overcrowding has remained a stubbornly persistent feature of our prison system. More than 60% of the prisons in England and Wales are currently overcrowded, and reoffending rates for ex-prisoners are accordingly high: the most recent figures from the Ministry of Justice show that 48.5% of ex-prisoners are re-convicted of a further offence within a year of release.

A new approach is clearly needed. Taking concerted action to reduce the prison population would undoubtedly cut costs, but it would also free up space and resources within the prison system to better rehabilitate those who have committed serious offences, and who do need to be there. It would, additionally, mean that the Ministry of Justice's budget - which, as Mr Khan points out, has been significantly reduced - could be more clearly focused on community interventions, which we know are more effective at reducing reoffending. Ministry of Justice analysis has demonstrated that those receiving community orders have lower reoffending rates than those given custodial sentences of twelve months or less, with the difference a significant 8.3% in 2008.

In its green paper 'Breaking the Cycle', the Government set out proposals that aimed to reduced the demand for prison places by 6,000 and the prison population by 3,000 over the spending review period. Though the 50% discount for the earliest guilty pleas has subsequently been abandoned, and the new plans aim to reduce demand for prison places by a rather more modest 2,650 by the end of 2014-15, there are a number of measures in these proposals that could have an impact. These include removing the option of remand for defendants who are unlikely to receive a custodial sentence; diverting those with mental health problems away from the criminal justice system; and the widespread implementation of restorative justice, so that it is firmly embedded at every stage of the criminal justice system.

All of these measures could help to reduce the prison population, and this is to be applauded. As well as helping to reduce costs, imprisoning fewer people will help to reduce reoffending, and so will enable us to take the first important steps towards a rehabilitation revolution.

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