The Duchy of Cornwall (DoC) will continue to receive millions of pounds over the coming decades from renting out HMP Dartmoor to the government, it has emerged - even though the prison is not in use and may never reopen.

The Grade II listed prison has been closed since last year, when all 682 inmates were moved out after high levels of the radioactive radon gas were detected. Only a skeleton staff remains on site.

The DoC, which owns the 215-year-old prison, leases the building out to the ministry of justice for £1.5m a year, but under the terms of the agreement (similar to the one the Duchy has with the Dartmoor National Park Authority for the Princetown visitor centre) it is not responsible for the upkeep of the facility.

According to a revealing report in The Times newspaper, the 25-year lease agreement came into effect in December 2023 and runs until Christmas Day, 2048.

But due to a “dilapidations clause”, the taxpayer will have to foot the cost of any repairs, which could be as high as £68 million.

Since its closure, the building has fallen into disrepair, reportedly leading to a rat infestation as well as damp and mould, according to a recent report by the prison’s independent monitoring board. It called for an “urgent decision” on the prison’s future, suggesting it may never reopen.

The government has reportedly spent £867,000 so far in an attempt to reduce radon levels, which were 10 times above the recommended limit in 2023.

The Times also quoted Baroness Hodge of Barking, saying that “profiting” from the prison while it remained closed had “the makings of nothing short of a scandal”.

She said “the time has come to look at alternative arrangements” for managing the DoC and the Duchy of Lancaster “and to bring them in line with bodies like the Crown Estate, which is overseen by the government”.

In response, a DoC spokesperson pointed out that the prison has been let to the ministry of justice since 1850, adding that as the ministry holds a full repairing lease for the facility, “it is the ministry of justice’s responsibility to undertake all repairs”.