Gregory is 50! Yes, really. You read that right. The lanky schoolboy from Cumbernauld in the west of Scotland – he of Bill Forsyth's fabulous coming-of-age movie Gregory's Girl – has just hit the Big Five-O. Or, at least, the actor who played him has. And for many of us reared on the 1981 film, this is vaguely shocking.
Not that life's ticking clock seems to bother John Gordon Sinclair over much. True, he has hardly had the greatest of half-century celebrations. The botched legacy of an appendix operation when he was 12 required extensive stomach surgery around the time of his last birthday, and put him out of circulation for the best part of six months.
It cost him a belter of a role, he smiles ruefully. He was poised to take over from the award-winning Bertie Carvel as Miss Trunchbull in Tim Minchin's accolade-laden West End production of Matilda when he was asked to try out one of the more energetic scenes. He had to 'fess up to the surgery, and accept that the rather juicy part was beyond him.
Sinclair's done well enough as an actor – he's had award-winning roles in stage musicals such as She Loves Me and The Producers, and will be seen next year with Brad Pitt in the post-apocalyptic thriller World War Z. But Gregory's lofty frame and cheery, feckless disposition have cast a long shadow. And, you surmise, may have cost Sinclair some roles.
"I'm proud of Gregory's Girl, and if I had never done anything else in my life, well, that would be enough. But it did tend to define me. It's everyone's first impression, and I've spent years trying to convince people that's not who I am."
Nor – and this might seem odd coming from someone who had a long, luvvie-type relationship with ultra-thesp Ruthie Henshall – is he entirely enamoured with the acting profession. They are, it seems, not his kind of people: "I always feel vaguely insulted when people call me an actor. I look on it as almost a derogatory term. I've never really thought of myself as one. Jane Horrocks is my one pal who is an actor, and the rest of my friends are the guys I came down from Glasgow with. I have always enjoyed the work, just not the stuff around it. I can't bear the 'luvvie, darling' thing."
So Sinclair – comic actor, star of musicals – has opted for another path: he has turned author. And his debut thriller, Seventy Times Seven, is something of a shock: it's pretty brutal. One scene involving a boiled kettle is almost unreadable. It's a fast-moving, wise- cracking story about two Republican brothers from Belfast caught up in the Troubles; about supergrasses, double agents, paramilitary brutality and SAS summary justice, set in Northern Ireland and in Nowheresville, USA. Its theme? Forgiveness, hence the title, derived from the Bible and Jesus's advice to Peter on how many times he should be prepared to forgive his brother.
Sinclair is entering a crowded market: Tom Bradby's 1998 novel Shadow Dancer, about MI5 and Belfast, has just been reprinted by Corgi to coincide with this month's release of the film starring Clive Owen and Andrea Riseborough. Even Ian McEwan's latest, Sweet Tooth, is set inside MI5 and against a backdrop of the Troubles.
So why the dramatic switch of careers? Late(ish) fatherhood is the key. (His wife, incidentally, is a doctor, and they live in Surrey.) "We've got two daughters now. Eva's six and Anna's four, and I just wanted to try to do something that allowed me to be around for them. I don't want to be one of these absentee dads, so I've turned down some roles that would have kept me away from home. A couple of years ago, a firm rang me up and asked if I wanted to write my autobiography. I wasn't terribly interested, but I did have an idea for a film script that became the book.
"I've always been fascinated by Northern Ireland. I remember coming down from Glasgow to live in London around the time of the Harrods bombing and wanting to try to understand what it was all about. I just read everything I could. Plus, friends of mine had friends there – Clare Grogan who was in Gregory's Girl is one – and I've been going to Northern Ireland since I was 18 or 19. I've had some of the best nights of my life there."
Seventy Times Seven is set in 1992, but a second novel will bring the story into the present day. He has to deliver the manuscript in December, and he grimaces. "I'm not the most disciplined of authors. I'll never be a sit-there-and-write-1,500-words-a-day guy. But once you realise that, and start to use the odd half-hour here and there to work, it can be very productive."
We meet just after Gregory's Girl has featured in Danny Boyle's opening ceremony for London 2012 in the sequence showcasing the best of British cinema. He is clearly chuffed, and the truth is that – despite his insistence otherwise, and his rather dapper frock coat with mustard lining – there's plenty of Gregory still to see in Sinclair: the mannerisms, the accent, the way he laughs.
"Of all the things I've done, I'm very proud of Gregory, and of being in The Producers. But I'm proudest of all of this book. It sounds trite, but I'm the producer, director and actor all in one. It's all down to me, and that's some achievement. An author is really what I want to be."
One last thing: my seven-year-old daughter, I confess to him, takes her name from Gregory's Girl. He looks confused. "Dorothy? Susan? Madeline?" None of these, I say, and, when I tell him, he is – not unreasonably perhaps – incredulous, and insists on writing a lovely note in a copy of the book for her. See YouTube, and the dressing-room scene, for the answer.
Seventy Times Seven, By John Gordon Sinclair
'Danny McGuire had received the call just a few hours earlier. The thin, guttural voice on the other end of the phone sounded older than he remembered, but was easily recognisable: Lep McFarlane ... Danny's instinct on hearing the thick Newry brogue was to hang up, but Lep was the last person to have seen his brother alive ...'