The new pounds 15m prison ship HMP Weare was floating empty of prisoners in Portland Harbour last night, less than two weeks after it took on its first inmates.
All 45 prisoners have been evacuated from the vessel, moored off the Dorset coast, and moved into more standard jail accommodation because the ship is a fire risk.
The episode represents a major embarrassment to the prison service, which gave the go-ahead to the floating jail despite concerns expressed by local fire chiefs.
The prisoners were moved out on Wednesday and spent a night in Verne prison at Portland before being transported yesterday to the Hollesley Bay prison at Woodbridge in Suffolk.
The only people on board the prison last night were a team of contractors who were working to repair the vessel's fire safety sprinkler system which was found to be ineffective.
The signs had not been good when the first 21 prisoners were moved onto the Weare a fortnight ago, the first British prisoners to be held on a prison hulk since Victorian times.
Within hours they were evacuated as the fire alarms went off. No fire was found and prison officials insisted that the vessel was safe.
But Frances Crook, director of the Howard League for Penal Reform, said the Weare was an "accident waiting to happen". Now she has been proved right.
David Wilson, senior policy adviser to the Prison Reform Trust, said: "According to the fire service, a fire on ship is the most dangerous and difficult fire to have to fight. We have always queried whether or not there were adequate contingency plans in relation to safety issues and our fears seem to have been justified."
In prisoner jargon, a transfer is normally referred to as being "shipped out". In the case of the Weare inmates, they have been "shipped in" for what could be a lengthy period of time ashore, although prison officials hope that they will be moved back onto the ship within days rather than weeks.
The vessel was bought in New York where it was awaiting sale for scrap for about pounds 300,000.
It was towed across the Atlantic and more than pounds 11m has been spent on converting a rusting barge, once used to house offshore workers, into a six-deck prison ship to house 400 low-risk inmates.
Cells are carpeted and have en suite showers, and there are sports facilities on board.
In April, fire chiefs expressed concerns about the thin walls between cells and the lack of emergency access to the ship.
A prison service spokeswoman said the sprinkler system had been found to be faulty after "accidental damage".
She said: "It was decided by Alan Walker, the director of operations (south), that it was in the interests of the safety of the staff and prisoners that they should be taken off the ship until the system was working properly again."
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