Scottish actor Martin Compston isn’t sweet 16 any more. The Line of Duty star has grown-up views about living in Trump America and the ties pulling him back home. By Paul English

Teenagers from the post-industrial town of Greenock, on the banks of the River Clyde, generally don’t waste time dreaming about the day when they’ll be phoning in interviews from the hammock of their back garden in Los Angeles.

Not even after they’ve been given a dream ticket by one of the most respected film-makers in the world.

Yet here’s Martin Compston, on the phone, in a hammock in the back garden of his Los Angeles apartment in 75˚F heat, talking about a film he’s just finished with Keira Knightley.

And still he has the good grace to laugh when I ask where it all went wrong. “Sweet Sixteen was a monkey on my back for a while,” says the actor, thinking back to his gritty turn in the 2002 Ken Loach flick that took Cannes by storm and scored him a crack at something altogether more fulfilling than the football career he might have had as one of a number in Greenock Morton’s youth ranks – steering him from Cappielow stadium to Hollywood. “As much as it was an incredible start, people actually thought I was that kid for a while.”

Not any more.

Yet as he loafs in the Southern California sun and prepares for the return of his BBC One network drama Line of Duty, the 32-year-old’s view of the past hasn’t been distorted by the Pacific coast heat haze.

There’s always something to look back on to keep my feet on the ground

He laughs at some of the chaff on his CV. Strippers vs Werewolves, for which Cannes didn’t come calling, will surely go on to achieve ironic cult status in time.

“Aye, there’s always something to look back on to keep my feet on the ground,” he says. But there’s plenty else besides. Since playing Liam, the young boy with the odds stacked against him in Loach’s study of life in a working-class community crippled by addiction and violence, Compston has stead-ily built a reputation as one of the country’s most popular turns.

Standout roles in indie flicks like 2006’s Red Road and The Disappearance of Alice Creed (2009), with memorable turns in Irvine Welsh’s Filth (2013) and A Guide to Recognising Your Saints with Robert Downey Jr and Shia LaBeouf, bring him to a point in his career where he’s onset with Keira Knightley and Alexander Skarsgard in Prague, and then resurrecting his role as anti-corruption cop DS Steve Arnott in Line of Duty, the most popular cop drama on British telly.

Graduating from BBC Two to BBC One after regularly pulling viewing figures of 4.5 million across its first three series, the show has enjoyed breathless reviews. But Compston expects the tide to turn – at least for himself – this time around.

“I’ve had a lot of praise but a lot of the media I’ve spoken to didn’t even realise I was Scottish. I think now that my profile has risen a bit – I’ll guarantee I’ll get a bit of grief for my accent this year.”

He stays in character for weeks while playing Arnott, lest his Scots tongue interferes with the London accent he works hard to maintain for the duration of the shoot.

I’ve had a lot of praise but a lot of the media I’ve spoken to didn’t even realise I was Scottish

“We’re now in the biggest slot in British telly, and I know I’ll be under a lot of scrutiny,” he says. “I try not to get complacent. With me, accents are like going to the gym, the harder I work at them, the better it gets. So I stay in that accent all the time because that way the cast and crew aren’t listening for mistakes. But people forget you can be doing a 25-page scene over eight hours and holding down an accent. It’s tough but it showcases another side of you.

“People ask me why I don’t play him as Scottish,” he adds. “I auditioned for a London detective. If I’d gone in with a Greenock accent I wouldn’t have got it.”

Despite the success and career consolidation of Line of Duty – it’s already been commissioned for a fifth series, before the fourth has even aired – Compston believes it was because of his film work that he was chosen by director James Kent to star in The Aftermath with Knightley and Skarsgard, his biggest movie role to date. Set in post-World War Two Germany, Compston plays a British intelligence officer.

“I’ve been really lucky with some of the people I’ve worked with, people like Keira, Alexander and Jason Clarke, who I was a really big fan of. But there were no airs and graces and every one of them took their craft very seriously and were very respectful. I really enjoyed it.

“There’s always a bit of you as an actor that feels like you’re playing at dressing up. When I put that waistcoat on in Line of Duty, it feels like I’m ready for business. Same with wearing war fatigues on these incredible sets. I just get totally swept away by it.”

Whenever I’m back in Scotland I stay with my folks. I revert back to being 15, with a Lisbon Lions top above my bed

It’s a long way from cleaning the boots of the first team at Cappielow Stadium – but despite marrying his American fiancée Tianna Chanel Flynn last summer in Greenock and living the sort of jet-set lifestyle many a footballer would envy, Compston’s still very much a home boy.

“Greenock is always going to be home for me, and one thing I miss about being away so much is seeing my nephew growing up,” he says.

When you’re on a run with this job, your personal life goes to shit

“Whenever I’m back in Scotland I go straight to stay with my folks. I revert back to being 15 again. I still sleep in my old bedroom, and I’ve still got a Lisbon Lions football top framed above my bed.

“We’re happy in America but we’re not always here. I still haven’t managed to give her a honeymoon, and we’ve been married for eight months. When you’re on a run with this job, your personal life goes to shit. You have to keep riding it when it’s going because there are a lot of better actors out there ready and waiting to step in. So you have to stay on your toes. But I have a high standard of work coming in and I’ll be heading home for work for the next couple of months.

“I’m still very much at home when I’m at home,” he adds. “But this is what Tianna and I signed up for, and we’ve always talked about coming home to Scotland eventually because that’s where we want our kids raised when the time comes.”

Compston is speaking to The Big Issue days before Nicola Sturgeon’s announcement of plans for a second referendum on Scottish independence.

He became a prominent Yes campaigner in the first referendum in 2014 – and while circumstances both personal and political might have changed, little else has on that score.

He says: “The London politicians are spectacularly out of touch with Scotland – even people like Jeremy Corbyn and Sadiq Khan, who I respect, are clueless. You have someone like Corbyn saying there’s no appetite for independence? It’s not about appetite, it’s about necessity. There was no appetite for a European referendum in Scotland and we had that forced upon us.

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“The 2014 referendum took a lot out of people but we also saw an incredible spirit and people engaged in healthy democratic debate.

“We lost it on very specific grounds. We were promised that Scotland as part of Britain would be part of the EU, and that isn’t going to be the case, so we have to look at that again.”

The left needs to get the finger out. We should have been ahead of Brexit and ahead of Trump

Now that he splits his time between Los Angeles and Inverclyde, he has a unique dual political perspective, experiencing life both under Donald Trump and heading for Brexit. Has he been tempted to wade in on politics Stateside?

“I have my views but I don’t have a vote, so it’s for people who have a vote to deal with. You can’t be preaching to them, it’s their country,” he says. “But the left, or at least the middle-left, needs to get the finger out. We should have been ahead of Brexit and ahead of the Trump situation. We always seem to have a rallying call after the fact. We’re in danger of becoming a protest movement.”

Line of Duty is on Sundays at 9pm on BBC One

@PaulEnglishhack