Read our Privacy noticeHundreds more inmates and staff could have been exposed to cancer-causing gas after government testing reveals nine prisons are battling to contain high levels of potentially deadly radon. That prompted hundreds of former prison staff and prisoners to sign up to a group legal action against the MoJ seeking compensation. Dartmoor has already been mothballed because of high radon levels. A spokesperson said: “We routinely monitor levels of naturally occurring radon gas across the HMPPS estate and take action to mitigate risks wherever elevated levels are identified.” Mlader Kesar, of law firm Kesar and Co, which is coordinating the Dartmoor legal action, estimates that there are now close to 900 claimants.