When you think about it there’s nothing more socialist than a prison: a publicly-owned, bureaucratic, micro-managed institution in which the state provides people with all their basic needs while regulating every aspect of their lives.

All part of the punishment, you might think. But prisons don’t just punish those who reside within their walls. For the taxpayer it’s a life sentence.

According to the Ministry of Justice, the average of cost per prisoner is nearly £35,000 per year. So, it’s true, it really does cost more to keep someone in prison than to send them to Eton (though, to be fair, prison does have a more socially inclusive intake).

The tougher sentencing reforms pioneered by Michael Howard in the 1990s led to a massive increase in the prison population – and therefore the overall cost to the public purse. But even in an age of austerity, right-wingers are extremely reluctant to countenance any change of course – as Ken Clarke found out during his recent tenure as Justice Secretary.

It’s not difficult to understand why. Tougher sentencing was a response to a decades-long surge in criminality – and the fact that crime levels subsequently diminished is taken as evidence that prison does indeed work. The idea of surrendering these gains just to save money therefore looks like a very literal case of robbing Peter to pay Paul – of transferring the costs of crime from the state to the streets.

But what if we could reduce our dependence on longer sentences without removing the downward pressure on crime levels? Does such an alternative even exist? The American economist Paul Romer believes that it does and makes his argument in a post for the Urbanization Project.

He begins by setting out a few basic facts about the situation in the US, which broadly parallels that of the UK:

“The homicide rate in the United States is now back down to levels that prevailed in the 1950s… The incarceration rate has peaked, but remains extremely high compared to the rate we saw then and the rate we see now in other countries. The new policy challenge is to find a way keep crime down while reducing the staggering social costs implied by our current incarceration rate.”

Romer’s key point is that we should assess the effectiveness of different punishment policies in terms of deterrence. Looking at the evidence, he comes to conclusion that longer sentencing is not necessarily effective sentencing:

“Punishment will have a larger deterrent effect if it is closer to the ideal of Swift, Certain and Fair (SCF). Making a punishment more severe, typically by increasing the length of a prison sentence, may add only a small amount of additional deterrence, or perhaps no additional deterrence at all. Longer sentences might reduce crime only by incarcerating people.”

In other words, if the only way that ‘prison works’ is by keeping people inside for a long time, then that will come at a cost. A “shift toward more swift and certain punishments” however could increase deterrence and therefore reduce the crime rate without pushing up the prison population.

Is there any evidence of this working in practice? Romer cites a comparison between the situation in New York and rest of the US. In the early 1990s, the homicide rate of the former was nearly twice that of the latter. There have been huge improvements since across America, but especially so in New York where the homicide rate is now lower than in the rest of the US. In both cases, the turning of the tide took place at the same time as a huge increase in the prison population. However, since the Millennium, the incarceration rate has fallen in New York – unlike the rest of America where it has remained at the Millennial peak.

New York, therefore, has maintained the downward pressure on crime while reducing its reliance on imprisonment. Romer ascribes this success to New York’s famous policing revolution – which among other successes has increased the swiftness and certainty of punishment:

“The reduction in the incarceration rate in New York state suggests that the increased certainty that can come from better policing can indeed reduce both the crime rate and the incarceration rate. They show that public agencies can learn to do their jobs more effectively…”

Ultimately, tougher sentencing is a poor – though expensive – substitute for effective policing.