Powers to control justice, policing and prisons should be devolved to the Welsh assembly as they are in Scotland and Northern Ireland, a commission led by the former lord chief justice of England and Wales has recommended.

In a strongly worded report on the justice system in Wales, a review chaired by Lord Thomas of Cwmgiedd calls for the age of criminal responsibility to be raised from 10 to at least 12 years, says “advice deserts” are appearing due to cuts in legal aid, and condemns high imprisonment rates as unsustainable.

The 555-page report, titled Justice in Wales for the People of Wales, sets out the findings of an independent study commissioned by the Welsh government in 2017. Commission members included Juliet Lyon, the former director of the Prison Reform Trust, legal academics, serving judges and a former chief constable of south Wales, Peter Vaughan.

The laws of Wales were codified in the 10th century during the reign of Hywel Dda, long before the English conquest of Wales by Edward I in 1282. The first UK parliamentary statute in modern times to apply only to Wales was the 1881 Sunday Closing (Wales) Act, which shut public houses in Wales on the sabbath – marking political acceptance of the separate identity of Wales.

The report’s most radical recommendation is the transfer of power from Westminster to Cardiff. It declares: “There should be legislative devolution of justice. Restrictions and reservations governing the [Welsh] assembly’s power to legislate on all forms of justice, including policing and offender management and rehabilitation, should be removed, so that it corresponds more closely with the position of the Northern Ireland assembly and the Scottish parliament. Responsibility for executive functions in relation to justice in Wales should be transferred to the Welsh government.”

A separate judiciary, up to the level of the court of appeal, should be established in Wales and the supreme court in Westminster should be required to appoint a justice with knowledge of the increasingly divergent laws of Wales in the same way it selects Scottish and Northern Ireland judges.

Thomas said: “The people of Wales are not well served by the current arrangements. Justice needs to be aligned with other policies and spheres of activity if it is to play the proper role it should in Wales. Devolution of justice functions is necessary. While the legislation is prepared, there is much that can and should be done to improve the delivery of justice in Wales.”

The report states: “Under the current scheme of devolution there is no properly joined up or integrated approach, as justice remains controlled by the Westminster government. Consequently, the people of Wales do not have the benefit which the people of Scotland, Northern Ireland and England enjoy by justice being an integral part of overall policymaking. There is no rational basis for Wales to be treated differently, particularly as Wales has its own long legal tradition.”

Thomas, who retired as lord chief justice of England and Wales in 2017, was a forthright and energetic reformer of the justice system, expanding the use of digital technology. He was one of three judges labelled “Enemies of the people” by the Daily Mail for their divisional court judgment in the first Gina Miller Brexit case. He subsequently condemned the then justice secretary, Liz Truss, as “completely and utterly wrong” for failing to defend the judiciary.

The commissioners identify significant problems in the existing system, noting that reductions in the justice budget “made by the Westminster government since 2010 have been amongst the most severe of all departmental budget cuts”. The Welsh government has used its own tax income to plug the gaps. “This position is unsustainable when the Welsh government has so little say in justice policy and overall spending,” the report says.

It says legal aid cuts imposed by Westminster have resulted in “advice deserts” where people are unable to obtain legal help, and increasing numbers of people are forced to represent themselves in court.

On the age of criminal responsibility, the report observes that “there are better ways to deal with children and young people than criminalising them … The current age of criminal responsibility at 10 is too young. It does not comply with United Nations convention on the rights of the child … We consider it should be raised to at least 12.”

The report calls for “problem-solving courts” to be established in Wales to provide more alternatives to imprisonment. Wales has one of the highest imprisonment rates in western Europe.

“The present rate of imprisonment is unsustainable,” the report says. “Money spent on keeping so many in prison should be used on other aspects of the justice system such as non-custodial measures as well as preventative work and legal aid, advice and assistance. Such an approach has proved successful in other western European countries and in some states in the USA.”