Radon in UK prisons: 42 sites under investigation after hazardous gas readings

On 26 March 2026, officials confirmed that radon in UK prisons is subject to a widening probe after the prison service disclosed 42 custodial and probation locations under investigation for elevated radon levels. The Ministry of Justice has already closed HMP Dartmoor following readings in 2024 that were about ten times above recommended limits, and the vacant site is currently costing taxpayers roughly £4 million a year while a lease remains in force.

Freedom of Information responses show at least 16 individual prisons have recorded readings above action levels, with named sites including HMP Exeter, Lincoln, Lindholme and Channings Wood. Records indicate parts of Exeter's D wing measured more than nine times the legal limit in 2020, and further monitoring from late 2024 into 2025 recorded concentrations exceeding 900 Bq/m³ in some areas. UK health guidance requires mitigation where workplace averages surpass 300 Bq/m³ and sets a lower 200 Bq/m³ threshold for sleeping areas. Radon is a colourless, odourless radioactive gas formed by decaying uranium in soil and rock and is linked to more than 1,100 lung cancer deaths annually in the UK, according to national health agency figures.

Legal action led by the law firm Kesar & Co relates to alleged exposures at Dartmoor and five other prisons — Exeter, Channings Wood, Lindholme, Portland and The Verne — and campaigners have pressed for detailed risk assessments. A ministry spokesperson said monitoring is routine and that mitigation is taken when elevated levels are identified.