The think tank’s assessment of prisons and probation, published on Monday, opens with the finding that “recent policy changes have put prisons back at risk of running out of spaces”. The change it identifies as decisive is the one the Prime Minister made in his first weeks in office.
Under the Sentencing Act 2026, passed by Sir Keir Starmer’s government, most adults serving a standard determinate sentence will now be released after serving a third of it, rather than at 40 or 50 per cent. A second group, previously released after two thirds, will leave at the half way point. The changes came into force on 1 October and are being phased in ten monthly tranches by sentence length, running to June 2027.
Burnham paused the scheme in July and then narrowed it twice. On 4 August people sentenced for rape, serious child sexual offences and grooming offences were excluded, affecting around 1,000 prisoners. On 30 August the Government added unlawful killing, which covers all forms of manslaughter, causing death by dangerous driving and causing or allowing the death of a child, together with the historic offence of indecent assault.
The exclusions were not made by amending the Act. The Government brought the release provisions into force for all offences except those on a published schedule, leaving the release dates of prisoners convicted of the excluded offences unchanged.
The effect has been to cut the number expected to be released early from about 6,000 to around 4,500. About 700 were freed on 1 October. A further 650 are due to be released today, in the second tranche, which covers sentences of between 574 and 883 days.
Murderers, and the most dangerous offenders handed life or extended determinate sentences, were already outside the scheme. Their release is decided by the Parole Board, so the exemptions did not keep them in prison. What they did was hold back a specific group of prisoners serving fixed terms, including two of the men convicted over the death of PC Andrew Harper. Albert Bowers and Jessie Cole, who were due for release next year at the half way point of 13-year sentences, are caught by the exclusion of unlawful act manslaughter. Burnham said when he announced the change that “the awful criminals responsible for the killing of PC Andrew Harper will not have their sentence shortened”.
The cost of that decision is counted in cell space. In September, free places in men’s prisons fell to just over 1,100, putting the men’s estate close to 99 per cent of its total capacity.
The report says the exemptions “may well wipe out such razor-thin margins and mean the Government is forced into yet more emergency capacity measures before new cells come online”, and forecasts that cell space will fall over the next 18 months.
Had the Act been implemented in full, Ministry of Justice projections suggest it would have put prisons on a “more stable footing”. Capacity would still have been extremely tight, at 97 to 98 per cent until at least 2032, and the upper range of population projections still exceeded estimated capacity. But for the first time in several years, forecast capacity was expected to consistently exceed projected prison population growth.
The Institute calls the reforms “set to be a real achievement of the Starmer government, especially in the face of significant political and public opposition”, before adding: “This progress has been imperilled by the Burnham government’s decision to exempt some prisoners from earlier release under the Sentencing Act.”
Prison building has compounded the pressure. More than 3,200 places have been added since 2024, largely through the opening of HMP Millsike in Yorkshire in March 2025, which brought just under 1,500 spaces, and the rollout of about 900 temporary “rapid deployment cells”. Because dilapidated or unsafe cells have had to be taken out of use, the net increase has been no more than a few hundred places.
A proposed “rapid” increase in places is not due to take effect until 2028. Capacity stood at 89,012 places on 5 October, higher than previously projected, largely because the prison service has postponed critical repairs, including fire-safety work. That work has to be carried out within 18 months. The Government now expects to reach its target of 90,000 places across England and Wales by November 2028, about a year later than planned.
The Institute also doubts Labour’s pledge of 14,000 extra places by 2031. In January 2026 the Government said it remained on track. The report says that, with cells taken out of use or lost to disrepair, the net increase will be substantially lower.
The Ministry of Justice has committed £110m to converting existing space inside prisons, including laundries, offices and storerooms, into cells. Mark Fairhurst, chairman of the Prison Officers’ Association, questioned where the staff to run any extra places would come from: “You can create as much additional space as you like, and build as many new prisons as you like, but where are the staff coming from to supervise people?”
A spokesman for the department said: “This government inherited a prison-capacity crisis after prison places increased by just 500 net places in 14 years. We are pulling every lever possible to fix that crisis, building 14,000 new places, accelerating the construction of additional cells, speeding up the deportation of foreign national offenders, and bringing the injustice of IPP sentences to an end.
“We will not let our prisons collapse ever again, and have already started publishing annual statements on prison capacity so we can ensure demand is never again allowed to outstrip supply. This is on top of our wider work to fix the justice system, imposing the toughest ever range of controls on offenders, and investing record sums in probation and victim support.”
Great British PAC reaction
Claire Bullivant, Chief Executive of the Great British PAC, said:
“What an extraordinary indictment of Labour’s priorities. We are now being warned that keeping murderers, rapists, child abusers and grooming offenders behind bars could leave the prison system facing another capacity crisis. Just think about what that says about the state of our criminal justice system.
“Protecting the public is not an optional extra. It is one of the most fundamental duties of any government. Victims deserve justice, families deserve reassurance and dangerous criminals should serve sentences that properly reflect the seriousness of their crimes.
“If excluding the most serious offenders from early release leaves our prisons without sufficient capacity, the answer cannot simply be to keep finding more prisoners to release. The answer must be to provide the prison places, resources and long-term planning that public safety demands.
“Labour has now been in government for more than two years. How much longer does it intend to blame its predecessors rather than take responsibility for delivering solutions? Where is the urgency? Where is the capacity? Where is the credible plan to ensure dangerous criminals remain behind bars? Where is their prison building?
“And while ministers grapple with prison overcrowding, they must also confront the pressures created by foreign national offenders in our prisons. The public are entitled to ask why those who have no right to remain in Britain are not being removed promptly wherever the law permits.
“Labour seems more concerned with accommodating those who enter Britain illegally than with ensuring we have the prison capacity, border security and resources needed to protect the British public.
“Labour cannot keep treating prison overcrowding as an administrative problem while expecting the British public to accept the consequences. Ministers are in government to make difficult decisions, not to lower public expectations of justice because the system is under pressure.
“A country that cannot guarantee sufficient prison space for its most dangerous offenders has got its priorities badly wrong. The British public deserve better, victims deserve better, and the Government must do better.“
