It’s not hard to see why Elizabeth Burton-Phillips had no inkling of her sons’ secret drug-ridden life. Her upbringing and adult life were a world away from the squalor of heroin addiction.

A small, kindly woman who teaches at a prep school in Buckinghamshire, she grew up in solid middle-class surroundings in Nottingham. Her father frowned on drinking, smoking and going to clubs.

“I remember once in the sixth form I asked if I could go to a disco. My father inspected my make-up and said I was wearing too much. But I can’t remember any conversation about the dangers of drugs.”

That innocence left her vulnerable when her twins Simon and Nick began to experiment with cannabis.

“When the boys set off on their bikes to school, my main worry was whether they had their books and had done their homework . . . not the local drug dealer. Looking back, what I wish is that I had had, as a mother, a much greater awareness of drugs in society.”

Shattered after Nick’s suicide, Burton-Phillips found comfort in her Christian faith. A year later she was coaxed by Theresa May, her local MP, into speaking from her heart to the Conservative Women’s Organisation conference at Westminster. She received a standing ovation.

That led her into talking to schools about her experience. At such events she distributes sealed envelopes to members of the audience. Inside, when she tells them to open them, they find a copy of Nick’s death certificate.

Writing about her son’s tragic, wasted life and the destruction it wrought on her and her family has been cathartic.

“I feel liberated,” she said. “It’s like I’ve got the stench of heroin out of my blood. Nothing will bring Nick back, but I’ve got something I can use for the greater good.”

And she is proud to say that Simon, her surviving son, is now free of drugs. They campaign against them together.

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