Fred and Rose West are among the most prolific and sadistic serial killers in British history. The couple tortured, raped and murdered at least 12 young women and girls before burying some of their bodies in the cellar, garden and under the bathroom floor of their home at 25 Cromwell Street, in Gloucester, between 1967 and 1987.

Kathleen Richards was one of the lucky survivors. Originally from Ireland, Kathleen, who was 17 at the time, knocked on the door of the "House of Horrors" with her 18-year-old sister Deirdre back in 1977. They had recently moved out of their parents house in Tredworth and were looking for a safe place to live. Little did they know that they were about to walk into one of the most infamous homes in history.

"Back in those days, it was very different. Our family was from Dublin and we moved here when I was 11. My dad was very domineering and strict," Kathleen, who is now 66, tells the Daily Express. "We were living in a two-bed house in Tredworth, Gloucester, with 10 of us altogether including mum and dad. As I got older, that was it. My dad wanted me to move out so the younger ones had space.

"I ended up at 25 Cromwell Street because, it's going to sound crazy, Fred and Rose West were well-known and well-liked in the community. I had heard through a friend of mine that said there was rooms to rent in their home and they're really cheap. I was pretty nervous being just 17, and very shy and innocent, but thought 'great I'll go for this room'."

Kathleen, the author of Under Their Roof, vividly remembers knocking on the door of 25 Cromwell Street for the first time. Her knock was answered by Fred, aged 36 at the time, who welcomed the sisters into his home.

"I knocked on the door and Fred West opened it. He had this grey suit jacket on and I asked if he had any rooms to rent. He said: 'Yeah, come in'," she explains. "I walked in and, on the left hand side, there was a room with the door shut so I didn't know what was happening in there. But the next room was his living quarters and I stood there at the doorway.

"In the room there were some children playing on the floor and Fred said 'these are my children and this is my wife' pointing at Rose West. He then pointed to a young girl, who looked around the same age as me, and said 'this is my lover'. When he said 'lover' I thought it was a joke but no one laughed. It was very strange."

Kathleen would go on to live in the "House of Horrors" for around a year. During that time she became subject to serious abuse at the hands of Rose.

However, there was one incident involving Fred that made her leave Cromwell Street for good. She recalls running out of the front door with nothing but the pyjamas on her back.

Kathleen explains: "I was in bed one day and woke up with Fred beside me. I was terrified. He wanted me go downstairs and watch a video with him and Rose.

"I said I'd be down in a minute and waited for him to leave the room. He said he would see me in a couple of minutes downstairs."

She continues: "I waited for the door to close behind him before jumping out of bed, in my pyjamas and with nothing on my feet, and running downstairs and going out the door. I never went back."

Fred and Rose West were arrested around 17 years later in 1994 after police got a search warrant to excavate their property. Fred was charged with 12 murders while Rose was convicted of 10, with many of the victims being young women, lodgers and family members.

Fred committed suicide in prison before his trial on January 1, 1995. Meanwhile, Rose was sentenced to a whole life tariff in November 1995.

One of their victims was 18-year-old Shirley Robinson who Kathleen built a close relationship with while living at the house. Shirley moved into Cromwell Street in April 1977 after meeting Fred at a local cafe.

Rose, who was pregnant at the time, boasted that Shirley was carrying Fred's child. However, she soon developed resentment of the teenager before she was murdered.

Shirley was then buried in the garden of the home and the remains of her body were found extremely dismembered. Her unborn baby had also been removed and had bones missing.

"I got quite friendly with Shirley. I remember one day she came home with sausage rolls and pasties and we decided to use the kitchen to heat them up," Kathleen says.

"We were using Fred and Rose's cooker but Rose came in and pushed Shirley out the way. We looked at eachother and left the kitchen straight away. Rose was very stern. I said to Shirley: 'She's not very nice is she' and she replied: 'Just ignore her. Just ignore her.'"

After Fred and Rose were arrested, police visited Kathleen after finding out she had lived in the house. It was at this point she identified Shirley as one of their victims.

"When police came to my door they showed me photos of the victims and I picked out Shirley. I said her name is Shirley Robinson," she explains. "I then went to court and helped convict Rose West. I told them that Shirley was there at the same time as me although Rose said she didn't know Shirley and had never met her.

"But she was in the living room when I turned up. She was there the whole time. She was murdered while I lived there. It was horrific to find out."

Kathleen explains how Fred and Rose displayed two differing personalities. On one hand, Fred was "jokey" while Rose was stern and strict.

Kathleen says: "It's going to sound weird but he was a kind of jokey character. Rose West, who was sat there when I first walked through the door, was really stern. She didn't smile at me and wasn't very friendly. But Fred was a jokey kind of man. So when he said 'this is my lover', you just think he was joking."

According to Kathleen, Rose "almost had two different personalities". She recalls one occasion where her mum visited the home and a switch flicked in Rose.

"She'd sometimes come through the door and shout at you but other times she sounded like a child," Kathleen says. "She'd be really sweet. When my mum went into town she'd come past the house and would sometimes knock on the door to ask if I'd like anything from the shops.

"A couple of times when that happened you'd go from hearing her shouting at someone in the house to saying quietly and politely 'Kathy, your mum's at the door'. It was like a different person. I'd often stay in my room to stay away from her."

Such was the conveyor belt of visitors, those who lived at 25 Cromwell Street never knew how many people were actually in the house. Kathleen recalls seeing a number of young girls come and go from the property.

"I never knew how many people were in the house at one time. You'd never know who was a lodger and who was a visitor. There were people in and out all the time," she says.

"They were mostly young girls and you'd just say hello as they walked in. That was it. You'd never know who was living there. There'd often be policing knocking on the door because someone reported the house for drugs. They'd ask if Mr and Mrs West were in and I'd say I wouldn't know as they were in a closed room."

Despite everything that took place in the "House of Horrors", Kathleen says she never considered that the couple were sadistic serial killers.

When asked if she had any happy memories in the house, Kathleen said she did. She was young and, for the first time in her life, free from the control of her father.

"I was free and I wasn't working. I'd go and meet friends in town and it was a happy time. It's the strangest thing when you look back on it. I had no idea what was happening. My dad was strict so it was the first time I had freedom. I enjoyed it."

Kathleen first heard of the horrors almost 20 years after she lived on Cromwell Street. She was in her kitchen and heard the story breaking on the radio.

"I first heard it on the radio in the kitchen and walked into my living room to watch the news on the TV," she says. I couldn't breathe. I felt sick. My first thought was 'how come I didn't know that? How come I didn't see that?'

"I must have been asleep or something. But then I thought 'how did I know?' I still have guilt to this day but I'm working on it."

Kathleen published her book last year and hopes it will help others who have been abused. She is hoping to work with charities to help victims in the future.

She says: "I really want my story to make a difference to people in the future. The worst thing is holding these things in your head for years."