MOST people know little of the criminal justice system. They probably hope it stays that way.

It might come as a surprise, then, to learn that if Scotland was part of the United States, its imprisonment rate would be equivalent to that of Texas or Louisiana. Or that according to recent data, the proportion of Scots jailed or on probation is among the highest in Europe.

Scotland, so often proud of its progressive credentials, has – much like England and Wales – a troubling relationship with law and order.

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Earlier this week, controversial plans to create a presumption against prison sentences of less than 12 months were pushed through by MSPs on Holyrood’s Justice Committee. The proposals – opposed only by the Tories – will now go before the Scottish Parliament, where they are expected to be passed into law.

Critics view the move as a betrayal of victims. They point to comments made by Lord Turnbull, a former chair of the Scottish Sentencing Council, who said it could include those currently sentenced to 18 months in jail due to the discounts applied to early guilty pleas. Some of these are serious offenders: drug dealers, killer drivers and people caught with child pornography.

On the other side, supporters point to the importance of rehabilitation. Short spells in jail don’t turn lives around; community sentences just might.

Justice Secretary Humza Yousaf told MSPs the “evidence for the progressive reform is absolutely overwhelming”. He insisted the current presumption against prison sentences of less than three months, which has been in place since 2011, had contributed to a fall in reconviction rates.

“We have to take Parliament and the public with us on a radically different journey when it comes to our punitive policy,” he said. Extending the presumption is not a silver bullet, but part of a “broader, evidence-led, preventative approach”. It is not a ban, and the judiciary still has the last word.

The trouble is, it’s not clear the latest change will be any kind of bullet at all. Just a week earlier, MSPs heard very different evidence.

Professor Cyrus Tata, director of the centre for law, crime and justice at Strathclyde University, told the committee the plans are really just a rehash of old ideas.

He said it amounts to asking judges not to hand out short prison sentences unless they think it’s appropriate. “Who passes a sentence that they think would be inappropriate?” he asked, not unreasonably.

Professor Tata is sceptical the change will make much difference. He also accused the Scottish Government of making “rather dodgy” claims by crediting the presumption against three-month sentences with a fall in reconviction rates. Meanwhile, the “shockingly poor data” in Scotland makes it hard to compare current sentencing practices across the country.

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Modern Scotland, Professor Tata said, is essentially using prison in the same way the Victorians did – as a poorhouse, or “the last line of the welfare state”. And unless there is a major shift in funding towards community services, nothing will change.

Dr Sarah Armstrong, of the Scottish centre for crime and justice research at Glasgow University, took issue with claims community payback orders have lower reoffending rates than short sentences. The raw statistics do not take into account the history of the two groups, she told MSPs. Those serving community sentences generally have fewer convictions, and those in jail have often had brushes with the law before. “It is therefore a matter of comparing apples and oranges,” she said.

Similar concerns were raised earlier by Kate Wallace, chief executive of Victim Support Scotland. She said victims do not currently receive any information about what has happened to a perpetrator who has received a community payback order. If justice must be seen to be done, victims are being left in the dark.

Dr Katrina Morrison, a board member at Howard League Scotland, which campaigns for penal reform, told the Justice Committee she backed the change. But she warned “significant resources will be required to make it work” – not just in criminal justice, but in the areas of mental health, addiction, housing and employment. Scrapping short sentences is not a way to save cash, and the 12-month presumption will not, in and of itself, reduce reoffending.

The point of all this is to highlight the sometimes confusing evidence backing this change, and the rocky road ahead. Mr Yousaf admits it will have only a “modest” impact on prisoner numbers, while experts agree a shift to community disposals will require substantial investment if it is to be effective. It’s also unclear to what extent the courts will take the new presumption into account.

Scotland has seen a reduction in conviction rates in recent years and a fall in the number of short jail sentences handed out. But this trend was established before the three-month presumption came into force, and the Scottish Government’s own research found “little sign” the 2011 change figured prominently in court decisions.

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The only thing that’s clear is the thorny problems at the centre of Scotland’s criminal justice system won’t be solved by a presumption against sentences of less than a year. To be fair, ministers acknowledge that. Mr Yousaf said the high prison population is a stain on Scotland’s conscience. He wants a radical shift. But this requires radical action, radical funding and better data.

Professor Tata advocates creating a target date, after which there will be a “transfer of resources” to community services. A principle would then set out which cases should normally lead to prison, and which shouldn’t. He summed up the current situation: “Prison is the last resort; it becomes the default when nothing else seems to be there. Prison never has to prove itself; everything else has to prove itself.”

If Holyrood seriously wants to change this, it will be a mammoth – and expensive – task. Otherwise, as Professor Tata put it, we risk repeating the same old debate again and again.