A decision by the Ministry of Justice to sign a long-term lease on a prison contaminated with dangerous levels of radon gas is expected to cost UK taxpayers more than £100m, according to parliament’s spending watchdog. The lease for HMP Dartmoor was agreed in 2022 despite officials already being aware of elevated readings of the radioactive gas.
The assessment was published by the Public Accounts Committee, which described the agreement as a “catastrophic” failure driven by pressure to secure prison capacity during a deepening overcrowding crisis.
Prison Closed Despite Known Health Risks
HMP Dartmoor, a category C prison that held large numbers of sex offenders, was closed in 2024 after radon levels up to 10 times higher than recommended limits were detected in parts of the site. Radon is a colourless, odourless radioactive gas linked to around 1,100 lung cancer deaths a year in the UK, according to the UK Health Security Agency.
The committee said the government later acknowledged that elevated radon readings had already been identified at the prison in 2020, raising serious questions about why a 10-year lease was signed two years later.
Long Lease on an Unusable Prison
Under the terms of the contract, the Ministry of Justice cannot terminate the lease until at least December 2033. As a result, the HM Prison and Probation Service is currently paying around £4m a year for a prison that cannot be used, covering rent, business rates and security costs.
In addition, the government is committed to spending an estimated £68m on fabric and maintenance improvements at the Dartmoor site during the life of the lease, pushing the overall cost well beyond £100m.
Watchdog Condemns ‘Blind Panic’ Decision
Geoffrey Clifton-Brown, the Conservative MP who chairs the committee, said the handling of the Dartmoor lease represented a complete breakdown in decision-making. He said senior officials appeared to have acted “in a blind panic” to secure prison places, rather than negotiating a deal that protected public money and staff safety.
The committee rejected claims that the lease was justified by overcrowding pressures, arguing that known health risks should have ruled out the agreement altogether.
Years of Delayed Action
Radon monitoring at Dartmoor began as early as 2010, with further tests carried out over the following decade. Despite this, the prison continued to operate until July 2024, when the final 640 inmates and 159 staff were relocated.
In parliamentary answers last year, the Ministry of Justice confirmed elevated radon levels were identified in 2020, while earlier reporting indicated unsafe readings may have been detected as far back as 2007. The committee said these delays raised concerns over whether action could and should have been taken much sooner.
Legal Claims and Ongoing Investigations
More than 500 former inmates and prison officers are now pursuing legal claims against the government, alleging their health was put at risk by prolonged exposure to radon. The prison is owned by the Duchy of Cornwall, which leases the site to the Ministry of Justice.
An investigation into radon safety at Dartmoor launched by the Health and Safety Executive in 2023 remains ongoing.
Union and Government Responses
The Prison Officers Association welcomed the report, saying it was unacceptable that no senior figures had faced consequences for decisions that endangered lives and wasted public funds.
Appearing before MPs last year, permanent secretary Jo Farrar defended the lease, saying it was signed during an acute prison capacity crisis and before the full scale of the radon problem was known. The Ministry of Justice said the current government inherited a system “on the brink of collapse” and argued the decision must be seen in the context of severe overcrowding pressures.
