Government testing has found radon gas above the accepted “safe” measure at nine prisons. The Independent reported that hundreds more prisoners and staff may have faced exposure to the radioactive gas.
The newspaper obtained the figures through a Freedom of Information request. They list the prisons where recent tests gave cause for concern as of July 2026. The nine are Dartmoor, East Sutton Park, Exeter, Leeds, Lincoln, Maidstone, Parc, Portland and The Verne.
In March, The Independent reported that a Ministry of Justice list named 42 UK prison and probation sites with high radon counts. The latest figures single out the nine where recent tests raised concern.
The findings follow the closure of HMP Dartmoor in 2024. It had emerged that staff and prisoners there had faced radiation well above the legal limit for a prolonged period.
The Ministry of Justice said it had introduced mitigation measures at the affected sites. These include ventilation and fans to try to bring levels of the gas down. The department has also appointed radiation protection advisers to manage the risk, as workplace laws require.
A spokesperson said the department routinely monitors radon across the HMPPS estate and acts wherever it finds raised levels.
Sarah Rigby, assistant general secretary at the Prison Officers Association (POA), said there was still no final decision on Dartmoor’s future. She said the union hoped HMPPS had learned from past mistakes in how it mitigated radon risk. She also referred to the full HSE investigation report into Dartmoor and the censure HMPPS later received. In her view, these showed that POA members had been right to worry.
Radon is a natural radioactive gas with no colour or smell. It forms when small amounts of uranium in rocks and soil decay, and it can build up indoors. Ventilation can control it.
The gas raises a person’s risk of lung cancer. Radon accounts for more than 1,100 deaths from the disease in the UK each year. Symptoms of radon poisoning include wheezing, fatigue and coughing up blood.
