When the Ministry of Justice (MoJ) released figures this month comparing reoffending rates, commentators fell over each other jumping to conclusions. According to the MoJ, longer sentences (of two to four years) resulted in a lower rate of reoffending than shorter sentences. Community orders and suspended sentences also led to less reoffending than sentences of under a year, but most newspapers chose to ignore any fact which might have obstructed their inalienable right to call for stiffer sentencing.

The biggest predictor of reoffending is not length of sentence but age. Inmates released after a four-year term are older and their offending goes down accordingly. They have also had the benefit of interventions which those serving short sentences do not enjoy. In addition, they are supported on release by an offender manager.

The MoJ research could have confounded the pundits if it had investigated other factors. For instance, when services are extended to provide help finding jobs and housing on release, reoffending drops. This is true whatever the length of sentence. It is also proven that facilitating consistent family contact during a sentence increases the chance of successful resettlement: this, too, is unrelated to length of sentence.

Since the figures prompted predictable calls for more sentences, longer sentences and tougher jails, let's look at a nation where exactly that formula has been applied. The US began to follow the path now prescribed by British commentators at the end of the last century.

Where has it led them? Well, first to the highest incarceration rate in the world. According to research by King's College London, in 2009 there were almost 2.3 million Americans in jail: that is more than 756 prisoners for every 100,000 citizens compared with 153 in England and Wales – and our own incarceration rate is high compared with most of Europe.

Thanks to a zero-tolerance approach to drugs and a policy of three strikes and you're in (for life!), petty criminals and small-time drug dealers are incarcerated for the long-term with the dangerous and violent. Most people who study prisons agree that a stay in a US penitentiary is a horrific experience but there is, shamefully, no overall monitoring body to assess levels of assault and abuse within jails. An insider study of one anonymous prison discovered that over 20% of inmates had been raped. In some states it is legal to use dogs not just to sniff out drugs but to attack non-compliant inmates.

However, someone is gaining from the high prisoner numbers: the companies which are running America's privatised jails. Taxpayers' money has turned prisons into big business. They thrive on high inmate numbers and low staffing levels and for prisoners this can only mean a lot of lock-down. And in the privatised world, the prospect of seriously denting profits by cutting prisoner numbers is a disincentive to successful rehabilitation programmes.

Let's see if the UK pundits calling for us to emulate the American system are right. How effective are longer sentences, a tough work regime and hellish jail experience when it comes to cutting crime in the US? The answer is no more effective than our own. Half of US prisoners are back inside within three years and two-thirds are rearrested in this time. No surprises there. I've never yet met an offender who was deterred from crime by the length of sentence.

I hope our government will have the guts to ignore the vengeance-hungry press and public who read a few statistics and think they know how to run a jail. Money spent on banging people up for years or on punishing community payback is money thrown away because offenders come back again and again.

Economics alone means that our penal system should be based not on punishment but on rehabilitation to cut the crime rate instead of detaining the same people over and over again. Can we afford the $49bn (£30.2bn) the US spends on running prisons? Let's keep the American model where it belongs – across the Atlantic..