Watching a dad say goodbye to his kids and knowing what is about to happen.. I got very emotional

that Colin Caffell said she absolutely captured the essence of Sheila.”

Cressida says: “I felt a huge responsibility. I wanted to make it as honest as I could. Looking at how mental health was treated then, it’s so different to now. The way she was labelled I thought was so shocking. She was a very vulnerable person.”

Colin says he knew Sheila would never have been capable of the murders. He recalls: “Once people explained the circumstances to me, I said, ‘Sheila couldn’t have done that’.

“She had never picked up a rifle in her life and certainly never knew how to fire one or load one. As a mother to the twins, she was always kind and loving, playful, like a lioness with her cubs, never ever angry with them.

“People forget the details of this case, but so many have stuck in their mind the impression that Sheila was a drug addict. She was not a drug addict. Sheila was very subdued by her prescribed medication. I know this has to work as a drama. They have done it very well. It exonerates Sheila.”

He also feels that Freddie Fox does a great job playing the killer.

Colin, who wrote In Search of the Rainbow’s End about the murders, says: “Freddie’s portrayal of Jeremy Bamber is scary. He read Jeremy’s letters that are in my book and he said, ‘I’ve got him’. He is brilliant.” Colin remarried and became a father again, moving to Cornwall to start a new life as a sculptor and potter.

He is prepared for the story to resurface when the drama is screened next month. He says: “I’m fully supported by my family so I’m not worried.”

Freddie, 30, was asked by people campaigning for Bamber’s release to meet them before playing the role, but turned down the invitation. He says:

CRIME SCENES Cressida Bonas plays Sheila Caffell Sheila with sons Nicholas and Daniel TROUBLED Sheila had health issues