An Irish woman who unknowingly rented a room from serial killers Fred and Rose West as a teenager has broken a near 50-year silence to share her extraordinary insight into the twisted couple’s lives.

Kathleen Richards, originally from Dublin, is one of the last surviving witnesses to life inside the ‘House of Horrors’ at 25 Cromwell Street in Gloucester, England, where six bodies had already been buried.

The Wests are two of Britain’s most notorious killers, who tortured, raped, and murdered at least 12 young women and girls – including members of their own family – between 1967 and 1987.

In a new two-part documentary on Virgin Media, Ms Richards speaks about moving into the Gloucester home at 17 years old in search of somewhere to live. She found herself living in an environment of manipulation, grooming and fear.

‘I definitely could have been one of those girls [who died]. I just wish I had never knocked at 25 Cromwell Street at all,’ she reflected. She said her family had left Ireland when she was a teenager, and she was living with her nine siblings and parents, while she worked at Walls Ice Cream factory.

When her sister had a baby, the two moved out with the child as their family home was too small. They heard of cheap rooms ‘up the road’ at Cromwell Street.

‘I knocked at the door. Fred West opened the door. I said, “Have you any rooms to rent” and he said, “Yes, come in”. He was a friendly guy,’ she recalled. She said they were introduced to his wife, Rose, and some children playing on the floor.

He then said: ‘And that’s my lover’, pointing to Shirley Robinson, who was about the same age as herself. Ms Richards said she didn’t believe him, as his wife was there too, adding that it was ‘weird’.

They were shown a room, and Ms Richards thought it would be great, given that a family lived in the house – never suspecting the evil that was present. She remembered seeing holes in the wall of their room, ‘peep holes’. She blocked them with newspaper, but the next morning the paper would be on the floor.

After a few weeks, she said, Fred West began to ‘grope’ her on the landing, telling her he was ‘just having a laugh’.

‘I was just thinking, “I don’t really like this game”,’ she said, adding that he was just a ‘dirty old man’ like others she’d encountered in the 1970s.

The documentary heard this was a key moment, in which West was exploiting Ms Richards’s vulnerability and his own power as a landlord, and teaching the naive teen how the household worked.

She said: ‘I thought I had found a place to call home, but no, I walked straight into danger.’

She said she began trying to avoid West whenever possible, creeping down the stairs and leaving the house as quickly as she could. Ms Richards said she was surprised to learn Shirley was pregnant, and that the baby was West’s.

They soon became friends. ‘I got the impression Shirley was a lost soul, but I think I was as well,’ she said.

She remembered a time soon after when West’s violence towards her increased, saying: ‘I was walking along the landing when Fred West came out of his room and grabbed me. He put me against the wall with his elbow at my throat. He started touching me. It was horrible. I was screaming; I was absolutely terrified.

‘Shirley came out. She shouted, “Fred leave her”, and Fred said, “I’m only messing about”.’

Shirley disappeared in the summer of 1978, when she was over eight months pregnant. Ms Richards said she remembered seeing Fred digging in the garden, and looking up and grinning at her.

It would transpire that Shirley and her baby had been killed and buried there, but Ms Richards was told that her friend had gone to stay with family in Germany.

She thought several times about going to the police, but thought she wouldn’t be believed. Then one night Fred came to her door, and asked her to come downstairs ‘to play a game’. She refused, but Fred and Rose West took an arm each and forced her down the stairs before sexually assaulting her.

‘I was like, “I can’t do this, I’m going to die”,’ she said.

The second episode will trace Ms Richards’s journey from her escape from Cromwell Street in the late 1970s through to the discovery of the murders in 1994.

• Surviving Fred and Rose West: Inside Cromwell Street airs on Monday, November 2 at 9 pm on Virgin Media PLAY and Virgin Media One