AFTER almost 35 years in the business, including a stint as a terrifying Coronation Street villain, Scottish actor Gray O’Brien rarely gets nervous.

Just before taking to the stage in one of the most-talked about Scottish plays of the year, however, he admits he was “having kittens”.

“I came in early to the theatre and had a wee look out on the stage, and suddenly, my heart was in my mouth,” he reveals, in surprise.

“That doesn’t happen very often. It was like I was back doing the O-level maths I failed three times, or sitting my driving test. I was panicking.”

Gray O'Brien as John RebusGray O'Brien as John Rebus (Image: Nobby Clark)

Gray is starring as fictional-detective-of-the-moment John Rebus, as Ian Rankin’s famous character continues to evolve from its globally successful literary beginnings into TV drama (the most recent, starring Richard Rankin, was a huge hit) and a stage play.

The latter is Rebus: A Game Called Malice, an Agatha Christie-esque drawing room murder mystery, penned by the author (a completely new story, not adapted from any of the books), and it has already been warmly received by audiences and critics alike.

Gray, who was born in Drumchapel and grew up in Ayrshire, grins. “The response has been great,” he says. “As soon as I walked out on stage, got the first laugh, it was fine.

“I think the nerves came because - there’s quite a lot riding on it. Headlining a show, the buck stops with you. And 30 million books…that’s a lot…..”

READ NEXT: Glasgow actor on being in 'the big league' working with David Tennant

The play begins with a dinner party at an Edinburgh mansion where guests are involved in a murder mystery game created by the hostess. Among them is Inspector John Rebus, whose instincts kick in when things take an unexpected turn…

“Ian has written a really good, really clever play,” nods Gray.

The cast of the play, which comes to Glasgow later this monthThe cast of the play, which comes to Glasgow later this month (Image: Nobby Clark Photographer)

“It’s funny, there are modern references – one of the characters is an influencer, for example – but it’s a classic whodunnit…it’s a really slick comedy thriller, and Rebus is fun to play.”

Gray has played several detectives over the years, but his very first was in the gritty Glasgow cop show that gave him his big break. He made five Taggart films as DC Rob Gibson, in the early 1990s, working with original lead actor Mark McManus.

“Mark was a very generous actor, I learned a lot from him,” says Gray. “I arrested Colin McCredie in one episode. And Sharon Small was my wife, in her first TV role. Happy memories.”

Gray wanted to be an actor from as young as five years old, he recalls. “I remember my careers officer at school laughing at me when I told him. As if a boy from Ayrshire couldn’t do that…”

He pauses.

“It’s that whole west of Scotland chip on the shoulder thing, isn’t it?” he says. “And I’ve been waiting, for the last 35 years, for someone to tap me on the shoulder and say - you’re found out son, off you go,” he says.

The cast of Rebus: A Game Called MaliceThe cast of Rebus: A Game Called Malice (Image: Nobby Clark)

“I’ve shared that with other actors I’ve worked with, and they always say after everything you have achieved, what more do you need to prove you have been a success?”

Gray studied at Glasgow’s RSAMD and he enjoyed huge television success, on Peak Practice, Casualty, River City and Doctor Who, and in Coronation Street, as murderous businessman Tony Gordon.

He surprised fans recently by revealing he had completed treatment for tonsil cancer. This November will mark five years since he finished chemotherapy at Glasgow’s Beatson.

“Having cancer was very scary,” he says, flatly. “The thing I worried about most was losing my voice.

“But I was very lucky. The team at the Beatson were wonderful and I’m delighted to be a spokesperson for them, raising awareness, telling people to get their lumps and bumps checked. Finding it early is important.”

READ NEXT: 'This is stupid': Slow Horses star takes to Glasgow stage to protest arts funding cuts

Gray is about to become a grandad, as his son Conor and his partner are expecting their first baby. He is over-the-moon happy, juggling work with decorating for the young couple as they move in to their first home. It has brought memories to the surface of the actor's own dad who died 24 years ago.

“My father had to sit through some dreadful stuff I did at drama school – I remember once, in a South African play, I was dancing about naked, covered in body paint…’

He breaks off with a laugh. “He must have been thinking - what the hell?

“But after my first Taggart, I went to see my parents and my mum said, 'your dad wants to see you, he’s in his shed.'

“I went to the shed, and my dad wasn’t tactile at all, but he gave me a hug and said ‘that’ll do for me, son.’”

Gray is momentarily overcome with emotion.

“I’d just been on his telly and he was proud," he says. "He was such a big Coronation Street fan, can you imagine how he would have felt watching his son become this massive, iconic character on that show? It would have been amazing.

"And now my son is about to become a dad…life goes in circles.”

Rebus: A Game Called Malice is at the Pavilion Theatre from September 23 to 27.