England and Wales prison spare capacity shrinks to 1,100 spaces

Headroom in adult men’s prisons across England and Wales stood at just over 1,100 spaces as of 28 September, down more than 200 on the previous week and 67% lower than at the end of April. Against that backdrop, the Institute for Government’s Performance Tracker 2026 assessment of prisons and probation reads less like a policy review than a balance sheet of a system whose liabilities have long outstripped its investment.

The most striking figure in the ledger is maintenance. In December 2024, the National Audit Office estimated the prisons maintenance backlog at £1.8bn, with a further £1bn required by 2030 to bring the whole estate into “fair condition”, including making all cells fire safe. The cumulative maintenance budget across 2024/25 and 2025/26 was just £520m, well short of the sums required. The consequences of that underfunding show up directly in operational capacity: cells taken out of use for dilapidation or safety concerns have largely cancelled out new supply. Around 3,200 new prison places have been added since 2024, largely from a new prison opened in March 2025 (1,500 spaces) and temporary rapid deployment cells (around 900 spaces), yet the net increase in capacity has been negligible, a few hundred spaces at most.

The capital programme itself is behind schedule. Both major expansion projects delivered since 2024 were initiated and largely delivered by previous Conservative governments, and constructing a new prison currently takes at least seven years. The pipeline has slipped, with rapid expansion of places now not due to start until 2028 rather than early 2027, partly because of delays to planned fire safety works. The government is not projecting to hit 90,000 prison spaces across England and Wales until November 2028, around a year later than planned. A key driver was commercial: the collapse of supplier ISG in September 2024, which was the main contractor for 17% of the Ministry of Justice’s planned additional spaces. In 2025, the National Infrastructure and Service Transformation Authority downgraded three key prison expansion projects from amber to red, meaning successful and timely delivery “appears unachievable”.

The financial exposure extends to safety. As of 2024/25, 44% of cells did not have suitable in-cell fire detectors. Recorded fires in prisons rose 124% from 2019/20 to 2024/25, with more than 500 fire-related injuries in each of 2023/24 and 2024/25. The Crown Premises Fire Safety Inspectorate issued eight prisons with ‘Step Away’ notices between August 2024 and June 2026, indicating it would pursue criminal proceedings were publicly run prisons not immune from prosecution over fire safety. The Starmer government abandoned plans to remove prisoners from non-compliant cells by the end of 2027 and set no new deadline.

On the demand side, the Sentencing Act 2026, based on David Gauke’s independent sentencing review published in May 2025, was designed to put prison demand on a more stable trajectory. Full implementation would have kept prisons at 97 to 98% capacity until at least 2032, but for the first time in several years forecast capacity was expected to consistently exceed projected population growth. That calculus changed when the Burnham government, facing public backlash, paused the progression model days before its September start, then exempted people serving sentences for rape, serious sexual offences against children, grooming offences and, later, unlawful killing. The changes are expected to reduce the number of people released earlier under the scheme from around 6,000 to around 4,500, thinning the supply of headroom the reforms were meant to generate.

Probation presents a parallel capacity problem, and one the reforms shift risk onto. The number of probation officers has consistently run 25 to 30% below target staffing; as of March 2026, nine probation delivery units, 8% of the total, had vacancy rates of 40% or more. Despite recruitment drives, practitioner numbers have risen only 3% since June 2024, and the government expects the supervision capacity gap in 2026/27 to remain over 20% of target staffing, equivalent to around 3,150 full-time employees, with target levels not expected before September 2027. HMPPS has instead set a goal of reducing workload by 25% by March 2027, through programmes such as Probation Reset and the Impact programme, which suspend contact with most offenders after just 16 weeks of supervision.

Technology spending is the other lever. Under Starmer, the MoJ committed up to £4m to expand the in-house Calculate Release Dates service into a fully end-to-end system, with court data flowing straight into prison records, within two years. That ambition follows a sharp rise in releases in error, which more than doubled in 2024/25 compared with the previous year, driven by complex rules applied across incompatible systems. Reviewers note the end-to-end goal is extremely ambitious given the limitations of Common Platform, the criminal courts’ case management system. Meanwhile, HMPPS aims for roughly a 6% reduction in staff demand through Justice Transcribe and other digital tools, and the electronic monitoring service, which the progression model relies on heavily, is already underperforming: from January to April 2026, only 62% of tags were successfully installed within two attempts, more than 5,000 people who should be monitored are untagged, and almost 1,600 are wearing tags that have not sent a signal in 14 days.

The returns on past investment are nonetheless visible. The breathing room from October 2025 to June 2026 coincided with the first declines in protesting behaviour outside the pandemic since 2012/13, with incidents at height down 15% and barricades down 11%, and self-harm and deaths down 10% and 12% respectively in the 12 months to March 2026. But with prisons back above 98% occupancy, those gains are unlikely to hold. The report’s verdict is essentially fiscal: after years of successive governments failing to invest in capacity, whether cells, staff or supervision, the system is being asked to deliver more with less, and the margin for error, in both senses, has nearly run out. Whether the next spending round closes the £1.8bn maintenance gap, or simply refinances it, may decide how much longer that margin lasts.