Beneath signs reading Convicted and Lifers, and Welcome to Houseblock I, Claudia Sturt, the new governor of Belmarsh prison, poses for a photograph. “People in the prison service tend to stand with hands in their pockets,” she says. “It’s important to appear relaxed at all times.”

The air in the cell block is hot and stale, a grim reminder that we are in one of Britain’s most secure prisons. But Sturt, businesslike in a grey pinstripe skirt-suit and pearl earrings, seems entirely at home.

Sturt is something of a troubleshooter for the prison service. As the former governor of Dartmoor, she revolutionised what was one of Britain’s worst jails, overseeing its reclassification to hold category C prisoners. Even so, she says her transfer to Belmarsh in southeast London last October is “high stakes”, and she could be forgiven for feeling less than relaxed.

Tall, blonde, glamorous and aged only 38, she is responsible for locking up almost 1,000 of Britain’s most notorious criminals — the hate preacher Abu Hamza and train robber Ronnie Biggs among them — and oversees the terror suspects housed in the prison’s high security unit. “It could keep you awake at night if you think about it too closely,” she concedes.

Belmarsh is rarely out of the public eye. Last week seven of its detainees were on trial for an alleged Islamic terror plot to bomb targets in central London.

And with high-profile cases comes unwelcome publicity: in January the prison was reportedly on the brink of race riots after a gang called the Muslim Boys allegedly tried to convert other inmates by threatening them with razors. Earlier this month an alleged delay in baton training for staff led Colin Moses, chairman of the Prison Officers’ Association, to accuse Sturt of “running Belmarsh in a pink, fluffy kind of way, like a flaming holiday camp”.

It’s a big job; especially for a woman with only 13 years’ experience of prisons. Sturt graduated from Somerville College, Oxford, with a degree in modern history, and after her basic training as a warden became what she calls a “junior screwess” running therapy sessions with eight psychopathic men at Grendon prison in Buckinghamshire. “It was incredibly interesting and great fun. It was all about talking to them. I spent two years drinking tea and chatting,” she says.

She became governor of Erlestoke prison in Wiltshire as part of the Home Office fast-track scheme when she was only 35 and moved to Dartmoor in July 2003 amid a blaze of headlines. “Should the governor of Dartmoor really be wearing this?” screamed one paper, pointing to a skirt hemline “several inches above the knee”.

She shrugs when I mention Moses’s comments. “It was just a very cheap jibe,” she says. “I first came across the pink and fluffy thing when I was the first woman governor at Dartmoor. People still have an image of what a prison governor should be and it’s a man in his fifties.”

In fact Sturt is one of 31 women governors out of 138 in the prison service and says, despite the odd swearword, she has always been treated with respect. “In men’s prisons particularly it can be a great advantage to be female,” she says. “If you’ve got 1,000 men locked up by predominantly men, sometimes a male colleague will tell them to do something, and you get a stand-off. A woman will ask and they’ll do it. That can make life a lot easier for all of us.”

When Sturt introduced curtains to cells at Erlestoke she risked a volley of sexist criticism about girlie touches, but she is matter-of-fact. “Curtains aren’t about decor,” she insists, “it’s about giving people a decent night’s sleep.” She would like curtains and duvets for the hardmen at Belmarsh but it would be too expensive. “At night Belmarsh is lit up like a Christmas tree. If you never get a good night’s sleep, you’re not in the best of health, not learning well and not very nice for staff to manage.”

Sturt is careful to refer to the “people” held in Belmarsh; they are never inmates, criminals or prisoners. Married to an army chaplain, Sturt is Christian; her faith is central to her work. The first thing she did when she arrived at Belmarsh was take communion in the chapel: “I would never take on a prison without doing that. It sends out a powerful message that you are not just coming to be the managing director but that it’s a calling or a service you are coming to offer.”

She was drawn to the prison service after a season spent as a jillaroo on a sheep station in Australia (not many women there either). At night the only entertainment was the radio and she became gripped by reports that Aborigines were committing suicide in police cells. On her return to England in 1990 the news was full of the riots at Strangeways prison. She wrote to several prison governors asking what was going wrong. To her surprise, two invited her to visit and see for herself; she left “absolutely hooked”.