ITV’s new documentary about prolific serial killers Fred and Rose West will finally be aired on Thursday 21 February.

Fred and Rose West: The Real Story with Trevor McDonald, part of the channel’s “Crime and Punishment” season, was originally scheduled for 31 January but was pulled at the last minute for unspecified “legal reasons” and replaced with a repeat of a programme the veteran broadcaster had made about death row inmates in the United States.

The film marks a quarter of a century since human remains were found buried beneath the Wests’ terraced home on 25 Cromwell Street on the outskirts of Gloucester, a discovery that brought their vicious crimes to light, shocking a nation and seeing the property branded the “House of Horrors” by Britain’s tabloid newspapers.

Sir Trevor’s documentary is understood to feature an interview with Jayne Hamer, a former lodger to the couple who has never previously told her story.

Hamer says she was lucky to escape with her life after hearing screaming from the cellar in which the couple murdered 12 young women and girls, including two of their own children, between 1967 and 1987. At least eight of the victims were previously raped and tortured before being put to death by the killers, many of them picked up in the first instance at rural bus stops.

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Also featuring interviews with a relative of the Wests and the families of their victims, McDonald’s film seeks to understand why it took so long to expose their savage crimes and what part Rose played, asking whether she might have been the driving force behind their actions.

Belinda Mott, sister of Juanita Mott, who was murdered by the couple, appeared on ITV’s This Morning ahead of the programme’s original air date to call for the return of capital punishment.

“This is where the death penalty, I feel, is needed, when it is without a doubt, there is no doubt at all, she was involved because Charmaine [West, Rose’s eight-year-old stepdaughter] was killed whilst Fred was in prison and in Rose’s care,” she said.

“So there is no doubt, she is a killer. We were destroyed by it.”

Fred West took his own life at HM Prison Birmingham on New Year’s Day 1995 but Rose is still alive, now 65 and serving 10 life sentences behind bars after being found guilty of nine murders.

The tabloids, for whom Rose West remains a figure of morbid fascination, reported this week she has been put on a low-carb ketogenic diet by staff at HMP Low Newton near Durham in a bid to bring down her weight from 18 stone, warning her appetite for junk food risked leading to heart disease and type 2 diabetes.

The new one-hour film arrives at a boom time for true crime series.

Netflix has enjoyed particular success with the likes of Conversations with a Killer: The Ted Bundy Tapes and Making a Murderer while podcasts like Serial and Teacher’s Pet have found huge audiences and even succeeded in reopening investigations into historic cases.

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