Sandy Neilson is sitting next to his son Anthony and recalling the moment everything changed. “To begin with, Anthony was known as Sandy Neilson’s son,” says the actor. “Now I’m Anthony Neilson’s dad.”

It is more than 20 years since Sandy directed his son, then 17, in a production of Marat/Sade at Edinburgh’s Telford College. This time the younger man is directing his father in Realism in the Edinburgh International Festival. It’s a state of affairs they seem entirely comfortable with as they enjoy a pint — dad cider, son lager — in a rehearsal break at Glasgow’s CCA.

“Anthony has moved into an area that doesn’t threaten me,” says Sandy. “It’s an area that’s his, in which I couldn’t compete anyway.”

Casting his father in the play, alongside Stuart McQuarrie, Paul Blair, Louise Ludgate and others, was an instinctive choice by Anthony, but a writer/director who works in such an unorthodox way must require a cast that are prepared to trust his process.

As a writer, Anthony thrives on two things: a company of actors around him and a fast-approaching deadline. Where most playwrights put their pens down when rehearsals begin, Anthony does the reverse, writing everything within six weeks of the opening night.

This seemingly uncertain method does not alarm his dad. “I know that it can work and, having watched Anthony, that it does work,” he says. “I’ve been in some shows that have been so grossly under-rehearsed that it was like going on without a script anyway.”

The weight of evidence is on Anthony’s side. It was the method he used for The Wonderful World of Dissocia, his conceptually brilliant representation of mental illness. This acclaimed 2004 festival production is to be revived next year by the National Theatre of Scotland. And for all the personal stress involved in working like this, it’s the method that suits him best.

Even now, little more than a week before opening, Realism is still evolving. Anthony describes it as “a magical trip into the mundane”, the opposite of Dissocia in its theme, suggesting it is about sanity as opposed to madness. “It’s the other side of that coin,” he says. “I’ve set myself a difficult task at the outer edges of my ability.”

This year is special for his father for other reasons. A veteran of companies such as Fifth Estate and Communicado, he is celebrating 40 years in the business.

Anthony’s mother, Beth Robens, was also an actor, which meant a childhood spent in and out of rehearsal rooms and a formative lesson about theatre’s emotional power. “I saw my mother in The Widows of Clyth playing a woman whose husband has died and she lets out a big scream,” he says. “Because it’s your mother, it has a much more visceral impact on you.”

From an early age, Anthony had a gift for language. “His primary school barred him from entering the English prize because he’d won it so consistently,” recalls Sandy.

For Anthony, his calling as a writer was not so obvious, but theatre was in his blood. “For me it was the same as if my dad had been a plumber and I’d become a plumber,” says Anthony. “ I grew up with the Edinburgh festival.”

Anthony would go on to earn a reputation as a controversial playwright. It is no accident that his father has always been involved with left-of-centre theatre, Anthony recalls how several of his father’s productions, such as Donald Campbell’s The Jesuit caused a stir. He dedicated himself to drumming up a similar reaction today.

Growing up with parents in the profession also ensured he has no illusions about the financial prospects of the business. “We were skint quite a lot,” he says. “It means I’ve an expectation of being broke, so it wouldn’t be a huge surprise to me if that were to occur. I’m going to do it anyway despite the fact that I’m going to be skint — there is a pure artistic impulse in there somewhere.”

Realism, EIF, Royal Lyceum, August 14­19

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