Britain’s newest prison was understaffed and unsafe when it opened last year and is still struggling with a “chronic shortfall” of prison officers, a damning inspection report has found.
Hundreds of cells are still empty at the new-build prison HMP Millsike in Yorkshire, which is run by private contractor Mitie, despite the government scrambling to find prison space.
A new report by the independent monitoring board (IMB), which carries out prison inspections, found that the opening of HMP Millsike in April 2025 was “chaotic” with basic processes, such as locking doors and counting prisoners, not being followed.
The failings were exacerbated by consistent staff shortages and inexperienced staff at the privately-run jail being denied the opportunity to train in government prisons in advance of opening, the report said.
The remote location of the prison has made hiring difficult, and the prison is still running with a “concerningly low level of officers”, the IMB said.
According to Ministry of Justice (MoJ) statistics from July, the maximum capacity at HMP Millsike will be 1,468 when it is fully up and running. The category C prison for low to medium-security inmates now has an operating capacity of 1,158 cells with a population of 1,124 – meaning more than 300 cells are laying empty.
MoJ officials say it is important for safety reasons for new prisons to be opened up gradually, with staff needing to adapt to a new site and establish the culture and regime.
However the IMB said that, despite an agreement between the MoJ and Mitie that there would be an 18-month mobilisation period to get the prison up and running, this was then reduced to 12 months.
While the prison opened on schedule last April, its opening was “chaotic, with inexperienced staff not knowing what to do and how to work with prisoners”, the report found.
New staff were denied opportunities to train in government prisons ahead of Millsike’s opening due to objections from the prison officers’ association, the IMB said.
After the IMB escalated complaints about the state of the prison in December 2025, a new interim director was appointed in February 2026 to iron out the problems. Inspectors said that he helped turn the prison around, pausing the intake of new prisoners so problems could be resolved.
However inspectors warned against opening new wings in the prison while “there is still a shortage of trained staff”.
Ministers are scrabbling to find space in the prison estate to house criminals after partially U-turning on plans to release people from jail early to free up space.
Justice secretary Alex Norris has committed £110m to finding and converting existing space in UK prisons, such as turning prison laundries into cells.
Mark Fairhurst, of the Prison Officers Association, has warned that even if extra cells are found extra staff will still need to be found.
Rebecca Major, IMB Millsike chair, said: “It’s a challenge to set up a new prison and even more so for Mitie who are new to prison management. The Board found that HMP Millsike was unready, understaffed and unsafe. In our view, some of the difficulties stemmed from inadequacies in Mitie’s mobilisation team. Either they underestimated the task or were not sufficiently experienced to take it on.
“Since then we’ve started to see improvements, but underlying difficulties remain. Many of them stem from a chronic shortfall of officers.”
A Mitie spokesperson said it did not believe the IMB’s description of the prison at the time it opened was a “fair or accurate reflection” of the conditions at HMP Millsike.
“Since the prison opened, the overriding objective of our colleagues, working in challenging circumstances, has been to ensure that those within our care are treated with decency and respect, whilst creating a safe and secure environment that supports rehabilitation. We welcome the recognition of the improvements made since opening,” they added.
The MoJ has been contacted for comment.