It cannot be ideal that drugs are still so frequently detected in our prisons, and the illicit trade is known to contribute to conflict behind bars.

But we cannot straightforwardly assume a doubling in the number of inmates found using drugs since 2013 means substance abuse is twice as prevalent. On the contrary, it is likely that it means - as the Scottish Prison Service claims - jail staff are getting better at intervening to prevent substance misuse, and better at disrupting drug deliveries.

Strip searching, scanners and more vigilance at visits can all help prevent the arrival of drugs in prison. Yet many people will agree with the Conservative justice secretary Douglas Ross that it is baffling that drugs are able to be brought into prisons at all. He says: “This is an environment which is meant to be absolutely secure,” but that is not the case.

We could make it so, but imposing absolute security would involve such intrusive and restrictive practices on all prisoners that it risks breaching their human rights. Perhaps more importantly, it would impede the positive relationships with staff which underpin good rehabilitation work. For example, regular full body searches of all prisoners, or bans on outdoor exercise and family visits might help cut the prevalence of drugs, but at a cost.

Mr Ross is right, however, to say that widespread drug use can also obstruct the ability of staff to work to cut re-offending. In that case, we should welcome the fact that prisons believe they are making progress, with only just over a quarter of prisoners leaving the jail with illegal drugs in their system, even though three quarters test positive for such drugs on arrival.

The SPS should continue to seize the drugs they find, while improving security and holding prisoners to account. But they should also continue to ensure treatment and detox services are provided, to help those for whom prison remains an excellent opportunity to confront and overcome an addiction.