Prison reform should be very high on the new justice secretary’s agenda.

It should not be surprising that Liz Truss has paid more attention to prisons than courts during her first few weeks as justice secretary. She will have been told that prisons have the potential to go badly wrong at a moment’s notice.

On the other hand, there are huge financial savings to be made if she can reduce the prison population of 85,000 to something approaching the 65,000 at which the figure stood 15 years ago or, better still, the level of 45,000 achieved little more than 25 years ago.

If there was any point in taking prisons out of the Home Office in 2007 and giving offender management to the new Ministry of Justice, it was to ensure that the courts could support a humane and effective prisons policy.

That is why there was such concern last month when it appeared that Truss was abandoning the commitment to problem-solving courts made by her predecessor, Michael Gove. Challenged directly about this on the Today programme, Truss said these courts were ‘a very good idea’ and that she was ‘looking very closely at plans for them at the moment’.

It was not a firm commitment but it was better than nothing.

Problem-solving courts create links between specialist judges and the support services that work to stop people having to face further proceedings. In England and Wales, the best known of these is the Family Drug and Alcohol Court pioneered by Nick Crichton when he was a district judge in London. Mothers who’d had a succession of children taken away from them at birth were offered tough love: conquer your addictions with the support of the court or your future children will continue to be be taken into care.

Are these courts cost-effective? Solicitors interviewed by the Gazette in May were unimpressed, pointing to the closure of the North Liverpool Community Justice Centre in 2013. But a review of the available evidence published by the Centre for Justice Innovation suggests that some problem-solving courts – though not all – achieve their aims. The centre, set up to support initiatives of this kind, finds that adult drug courts reduce substance misuse and reoffending. And family courts can reduce the number of children removed from mothers.

For juveniles, though, specialist drug courts may have a minimal or even negative effect on offenders. That happens when well-meaning judges overdose young offenders with multiple requirements, drawing greater numbers into the criminal justice system. As the centre says, problem-solving courts are not silver bullets: ‘The impact they can have on reoffending is positive but it is also modest.’

So let us consider another big idea that is current at the moment. Restorative justice brings together offenders and victims, with the consent of both. According to the MoJ, it enables ‘everyone affected by a particular incident to play a part in finding a positive way forward’. But the government insists that where a ‘formal criminal justice response’ is appropriate, restorative justice must be an add-on rather than a substitute.

You can see why some victims of crime may be reassured to see that ‘their’ offender is showing signs of contrition. Equally, some offenders will benefit from being confronted with the effects of their behaviour. Victims may achieve what they regard as closure while offenders may have the opportunity to make amends.

But what matters is whether restorative justice reduces offending. A report from the Commons justice committee suggests it does – although the evidence is not entirely convincing. ‘A commonly cited claim with regard to restorative justice’, the committee says, ‘is that, for every £1 spent, the criminal justice system saves £8.’

This turns out to be a massive over-simplification of an 80-page report which examined a limited experiment conducted a decade ago. As the MPs rightly say, ‘caution should therefore be taken not to place undue reliance on this figure’. But they find other evidence that ‘restorative justice can provide value for money by both reducing reoffending rates and providing tangible benefits to victims’. They want more of it.

Problem-solving courts and restorative justice are both worthy of support. But I suspect that neither of these projects are going to make much of a dent on the prison population. Rather more urgent are the 4,000 offenders still serving sentences of imprisonment for public protection, even though the IPP sentence was abolished in 2012.

Nick Hardwick, the new Parole Board chair, predicted in July that he could reduce this figure to 1,500 by 2020. It could be brought down still further, he said, if Truss were to make policy changes. No doubt MPs will question her closely about her reform proposals when she appears before the justice committee on Wednesday.