Name the country that keeps people locked up indefinitely, not on the basis of what they’ve done, but because of their personality traits? North Korea and Syria do their share, but so now, do we.

The length of a criminal’s sentence has traditionally reflected the severity of the crime. But what if criminals still poses a threat to society after they have served their sentence, such as in dangerous paedophile cases in the late 1990s? The Government’s answer was to create a new sentence of imprisonment for public protection, or IPP, under the 2003 Criminal Justice Act. The sentence can be passed only for a specific sexual or violent offence carrying a maximum sentence of ten years or more, and the court must consider that the offender poses a significant risk of serious harm. So what happens in practice is that two sentences are handed down. First, the “tariff”, which reflects the seriousness of the particular crime. Secondly, the indeterminate sentence, to reflect that the person is regarded as a risk.

And there’s nothing wrong with any of that, you may think. After all, no one wants vicious criminals out on the streets. But hold on. More than half of those imprisoned with IPPs were given tariffs of less than two years. Yes, we’re talking street robbers, low-level arsonists: nasty crimes certainly, but why are they being punished by what in effect could be a life sentence?

In order to get out of prison at the end of the tariff period, the offenders can apply to the parole board. It calculates risk on the basis of a forensic psychiatrist’s report and on a specific assessment of the individual. The problem for the prisoner is that the mainstream view among psychiatrists is that personality disorders – as opposed to mental illness – are untreatable. Critics say that people given an IPP risk serving a life sentence for a combination of committing a street robbery and being born into a deprived, dysfunctional family.

And the numbers being given these new life sentences are far greater than was expected, with well over 2,000 in custody. That has created an ever-growing rump of prisoners who may never be released but will increasingly clog up an already bursting prison system. So perhaps it is no coincidence that Lord Falconer of Thoroton is having to draw up plans to release up to 2,000 prisoners to make space.

Government policy is clear. People who are dangerous and convicted should stay in prison as long as they remain a danger. If we are to lock people up for their characteristics rather than their crimes, then we need to understand this new philosophy of imprisonment and be comfortable with the ethics that underpin it.

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