‘Concerns over therapy ferrets used to kill rats at UK’s largest children’s prison” was how the Guardian’s own headline reported recent events at Wetherby young offenders institution in West Yorkshire. “Concerns” felt pretty mild, and I’d have preferred to hear it was a panic or at least a flat spin.

I hoped that it had happened out of sight, since it is no small thing to watch one animal kill another, but that hope was immediately dashed by the detail that not only did the ferret attack the rat in front of its young inmate handler, according to a complaint from the Prison Officers’ Association, but it didn’t even finish the job. The grim scene ended with a prison officer stomping on the injured rat, prompting the National Ferret Welfare Society to side with both rat and ferret, in the statement: “We cannot condone the stamping to death of any animal in any situation.”

A rat in pain makes a surprisingly loud and human screaming sound. Trying to imagine how this scene could have been any worse, I got to: maybe if they’d put both rat and ferret in a cage, and affixed it to the young offender’s head. Maybe, in other words, if they’d specifically devised the incident as psychological torture, it could have been more torturous – but only marginally.

Vermin are nothing new in prisons: seven years ago, a 71-year-old man sued the prison service over the PTSD he said he’d suffered from rats running over his face and body every night of a short sentence in Wormwood Scrubs.

The most distressing detail from a crime and punishment point of view was that he’d been handed that sentence for benefit fraud (which he denied). Even if he’d committed it, the disproportionality makes you feel dizzy. It’s famously expensive, custody, and youth custody more expensive still; you can make the case for imprisonment to keep the streets safe, but meting it out for a financial crime of probably low order feels vindictive and socially self-defeating. More than that, you cannot imagine anyone in modern times thinking incarceration with rodents is fair. This ought to be a first principle of offender management: if you wouldn’t get away with it as a sentencing guideline, it isn’t acceptable as a side-effect.

An ex-governor of Wandsworth, who took over the jail after the turbulent 1980s, told me about its mouse problem when he arrived. This was an incredibly dark period in the prison’s history, when there was still slopping out, and prison officers went on strike, and the police had to come in to manage the prisoners, except they didn’t really have the skills, and the prisoners didn’t have a lot of skills either. What they did have was a readily available bucket of human excrement to throw at a door, with predictable results.

And still, the image that stuck in the governor’s mind was that if you went into the kitchens at night and turned the light on, it was like watching a grey carpet roll back as the teeming mice scattered. His conclusion was that it’s difficult to persuade prisoners that you care about them when you keep them in squalor; harder still to address their behaviour and prepare them for life after prison if they don’t think you care.

In the youth estate, where the prisoners must, logically, have been failed by multiple authority figures by the time they even arrive, the fragility of trust is greater, and the binaries of imprisonment are stark. It’s hard for custody to be a neutral experience. If it’s not helping, it’s making everything worse.

So this isn’t really about animal welfare, or public health, or therapy creatures, or even public sector outsourcing (although the vermin are often attributed to unsanitary conditions, with unions calling for services to be brought back in house). No idea is too radical – end incarceration of children altogether, end privatisation of public services, rebuild young offender management on a Finnish model. If you can’t manage children in custody humanely, then you are not fit to hold children in custody.