Dartmoor Prison may be breaching the Human Rights Act, according to the Prison Reform Trust (PRT).

The trust said in a new report overcrowding was stripping prisoners in Dartmoor Prison of their dignity and decency, and could compromise security.

At Dartmoor, 21 cells have been doubled-up to take more prisoners in conditions the trust says are not cramped, but unhygienic and unhealthy.

The Prison Service says the doubling of cells is regrettable, but it describes the report as "somewhat melodramatic".

Exeter's visitor board has criticised moving prisoners

Dartmoor, Exeter and Newton Abbot's Channings Wood prison are all mentioned in the report as being overcrowded.

Michael Long, chairman of the Dartmoor board of visitors, said: "Decency and dignity are being promoted by the director general. It's not decent and it's not dignified.

"For example, there is a toilet in the corner of (a) cell that has a flimsy curtain around it , which is really and truly far from adequate."

He said: "Another point is they don't have a chair, a table and a locker each.

"Double bunk beds take up a lot of room. The cell door doesn't open fully, so there also security issues there, and maybe issues that contravene the Human Rights Act."

Devon prison overcrowding

Exeter: 56% Channings Wood: 4% Dartmoor: 2%

Exeter is one of Britain's most crowded jails at 56% above intended capacity, nearly 200 more than its intended 316 inmates.

Exeter's board of visitors has also criticised the practice of moving prisoners great distances, causing distress and upsetting the balance of the prison.

Martin Narey, the director general of the Prison Service, said the doubling of cells was very regrettable and he took overcrowding very seriously.

He said overcrowding posed a serious challenge for the Prison Service but has not threatened security.

He continued: "However, the PRT report is somewhat melodramatic.

"A Prison Service producing a record number of educational qualifications, getting increasing numbers of prisoners into jobs on release and which is both decent and safe, is not a service in crisis."