THE latest play at The Almeida Theatre tackles the issue of drug use – among Islington’s middle classes.

Set in the upmarket streets and squares surrounding the theatre, The Knot Of The Heart tells how beautiful, privileged Lucy’s social drug habit turns into serious addiction.

David Eldridge’s family drama reveals how a charmed life can descend into chaos and how liberal attitudes to soft drug use can pave the way to ruin.

Muswell Hill actress Margot Leicester plays Lucy’s mother Barbara, a woman rarely seen without a glass of wine in her hand.

“It is using a classic middle-class Islington family to chart someone’s downfall from recreational drug use into massive addiction and, hopefully, recovery,” says Leicester.

“The play opens right in the middle of the problem, as Lucy is caught smoking heroin at the TV studios where she works as a presenter and is sacked. The audience is straight into the heartbreak that involves for her, her mother and sister.

“It’s a debate about unconditional love and how far parental and familial love protects a child but can also enable them to have a drug habit.”

Featuring doctors at The Whittington Hospital and a care worker at addiction intervention centre City Roads in Angel, the play examines the “tough love” approach to addiction.

It touches on contemporary debates such as the furore surrounding Julie Myerson’s 2009 book The Lost Child in which she describes throwing out her 17-year-old son when he became violent and abusive through cannabis use.

“It’s a prominent theory that you have to cut off all the support love and care for the person because only when they hit rock bottom will they get their own motivation for recovery,” says Leicester.

“The debate that Myerson underlines in the book is the painful dilemma for a parent in kicking out your child when your instinct is to say, ‘I will love you whatever.’”

In one speech, Barbara recalls discovering Lucy smoking pot with her teenage friends in the back garden and wonders whether she should have challenged it more firmly at the time.

“Barbara herself has a drink dependency, she’s always seen with a glass of wine in her hand, and the play asks is it just a socially acceptable form of drug use? As a woman who was young in the 60s, she did drugs and considered smoking pot par for the course.

“Although there is more awareness now about how cannabis can damage mental or physical health, for many middle-class people it hasn’t been seen as a harmful drug because it was tied up with notions of hippie freedom.

“Throwing people out of the house for smoking pot feels conservative, authoritarian and right wing – and anyway might that drive your kids out on to the streets where dealers are pushing harder drugs?”

As a mother of four grown-up children, aged between 18 and 26, Leicester brings her own parenting experience to her latest role.

“Thankfully, I have never been faced with the drug dilemma and I would find it an absolute nightmare if I was. But I understand that parenting is hard because you are only successful if you enable them to separate from you and lead their own well-adjusted, independent existence.

“In practice, that is difficult because you cannot shut them up and keep them safe. To get their own moral and emotional bearings, to learn how to negotiate their way in this world, might mean they have to go through dark and difficult experiences to get there.”

Leicester, whose CV includes work at The Donmar Warehouse, Hampstead Theatre and the West End as well as numerous screen roles, adds: “The writing is beautiful, very precise and exact. It gets to the heart of what the feelings surrounding this problem might be and is closely observed about the behaviour of the middle classes in a classy urban area.”

o The Knot Of The Heart runs from March 10 until April 30.