On Friday we reached a new record high prison population, at a time of year when prison numbers normally drop. This week 86,821 men, women and children were housed in prisons (including some 600 in immigration detention centres). Last Friday we broke a previous record with 86,654 people in custody. The week before the figure was 85,931.

Clearly the very large jump in numbers over the last fortnight is to do with the riots. But it's worth just thinking about the context of our ever-rocketing prison numbers.

Since the mid-1990s we have more than doubled our prison population. I joined the Howard League in 2007 and that year we reached 81,000 people in prison for the first time. Each year since, it has climbed higher and higher. The ever-expanding criminal justice system saw spending on law and order rise by the equivalent of half a percentage point of GDP between 1999 and 2006 to 2.5 per cent of overall GDP. We spend more than any other OECD country on law and order. But despite all of this, polling has demonstrated that 75 per cent of people in the UK feel there is more crime than last year and confidence in the criminal justice system is at an all-time low.

These latter facts are particularly frustrating for policymakers, given that recorded crime has fallen year on year for since 2000. Indeed, the fact that this has gone hand in hand with rising prison numbers convinced many, particularly in New Labour, that tougher sentencing was the right thing to do.
But Tony Blair's own strategy unit produced a report some years ago which estimated that a 22 per cent increase in the prison population accounted for only 5 per cent of an overall 30 per cent drop in crime. The substantial reduction came from benign economic conditions, improvements to home security and a dip in the second-hand value of many electronic goods. The same report stated that any further increase in the prison population was unlikely to contribute to any further reduction in the crime rate.

There is also plentiful international evidence which demonstrates that countries can experience drops in both the crime rate and the prison population. In Canada, for example, the prison population was reduced by 11 per cent in the 1990s while over the same period crime fell to its lowest rate for 25 years - including drops ranging from 23 per cent for assault and robbery to 43 per cent for homicide.

Similarly, New York City has seen both prison numbers and crime rates fall over the last two decades. At a time when NYC's population rose by 11 per cent and incarceration rates rose nationally by 60 per cent, the city's prison population had declined by 28 per cent and its crime rate has dropped by an average of 70 per cent - twice as much as the national drop in crime from 1990 to 2000.

The truth is that prison can be used to manage the problem of crime, temporarily incapacitating offenders and therefore making some contribution to reductions in crime. But reoffending rates - around two thirds for the majority of prisoners in the system, and a shocking 75 per cent for those under 18 - show that this merely delays the inevitable, and indeed a closer look at reoffending figures reveals that people become more likely to reoffend after each spell in prison. Many will reoffend far more seriously and frequently afterwards. Meanwhile, building more and more prisons to manage the constant expansion simply drains money from more effective solutions to crime. See the state of California, for example, which spends more on its prisons than on higher education.

Prison plays an important role in providing public protection from serious and violent offenders but it cannot tackle the underlying causes of crime. And here we come back to the riots. It is perhaps understandable that the courts are under pressure to treat the disturbances as an aggravating factor when sentencing offenders, although this should be balanced with a key principle of justice: proportionality.

But as the dust settles, it's time to change our thinking. We've doubled our prison population and seen tougher measures introduced each year, with an abundance of criminal justice legislation. Yet despite all this, the outcome of being "tough on crime" was some of the worst street disturbances seen in decades. That alone tells you that the answers to our problems do not lie within the criminal justice system.

Andrew Neilson is Director of Campaigns at the Howard League for Penal Reform