STEVEN Robertson has a poet's soul. As the mesmeric, lilting tones of his Shetland accent drift down the line, it's clear that the Lerwick-born actor is a born raconteur.

He is sharing stories about his childhood, the many eclectic jobs he had before becoming an actor and the enormous sense of pride that comes from seeing his island homeland showcased in a major television series.

Robertson, 41, will return to our screens in BBC Scotland drama Shetland this Tuesday reprising his role as sweet and dependable DC Sandy Wilson in a six-part murder mystery based on the bestselling crime novels by Ann Cleeves.

He lives in Hertfordshire these days, and the joy in his voice is palpable as he talks about heading back to old stomping grounds during filming. Robertson hails from the Lunnasting district on the north-east mainland of Shetland.

"I grew up on a croft and was always involved in agriculture," he says. "We had sheep – and I had my own sheep from a young age – which is something I have missed all the years I have been away. When I get home, especially if it is during the summer, I like to shear some sheep again.

"From when I was a little child I was lambing sheep and calving kye. After I left school my first job was as a dairyman. I milked cows and used to work summers on my uncle's farm. I'm very attached to the land in Shetland. All of that comes from my childhood."

While Robertson didn't harbour any ambitions of fame and fortune, there were early hints that his future life path may lie in performing.

"As a child I was very involved in the Shetland oral storytelling tradition," he recalls. "I grew up with this idea – a silly, romantic idea probably – that I was born in the wrong generation because I was fascinated by the history and the stories."

As a youngster he forged a close friendship with the late Rhoda Bulter, one of Shetland's most prolific and beloved poets. Bulter spent many of her own childhood summers on a croft owned by Robertson's family.

"I think it started during the war when they used to move children out of Lerwick at certain times of the year," he says. "Rhoda would come stay with my grand-uncle and grand-aunt. She fell in love with that area. I knew her because she would often come visit the croft when I was a little boy."

As he speaks, I'm trying to do the maths in my head. Bulter was born in 1929 (and passed away in 1994). She would have been in her mid-50s when Robertson first met her?

He confirms my hurried mental arithmetic with a laugh. "You would be surprised when I was a child by how many of my friends were a lot older than me," says Robertson. "I think that is island living. You have friends that are your own age and then friends who are in their 60s or 70s.

READ MORE: Shetland star Neve McIntosh on genealogy, Doctor Who and childhood heroes

"For some reason – probably because I was very interested in the storytelling and close to my grandparents – that age gap has never meant anything to me. I do think that is a small community thing too. People are people. You don't feel bracketed in that regard.

"It always felt that most people just talked to you, even if you were a little child of eight or 10 years old. If you wanted to learn an old Shetland story, then they would tell it to you as they would anybody else."

Was Robertson always a bit of an old soul then? "That is probably one way to put it," he says, chuckling softly. "Other people would say just a slightly eccentric child. But let's go with old soul – I think that sounds better."

He is appreciative that his conversations with Bulter left such an indelible impression. "Despite growing up with dyslexia, I always loved words, poems and books. Even at school I had managed to figure out a way to study Rhoda's poems as opposed to the likes of Ted Hughes or Shakespeare."

Immersing himself in the culture and rich storytelling tradition of his Shetland roots, reflects Robertson, helped him make sense of the larger world.

"I understood the stories talking about the lairds and the boats and some of the mystical stories we have to do with cows and other creatures," he says. "That all seemed real to me because I understood the landscape they were from.

"Even though I maybe didn't know it at the time, that was my route into an understanding of what you would perhaps call an artistic life or pursuit."

There would be a few more pit-stops on the road to discovering acting, though. After leaving school at 16, Robertson spent a couple of years milking cows. When the farm he worked on moved from dairy to beef production, he found a job as an apprentice violin-maker.

Next came a stint as a drum technician/nanny for the Shetland folk band Rock Salt & Nails. Wait, let's just rewind a moment. Can he repeat that job spec?

"I was a roadie, but also looked after the children that belonged to the guitarist and keyboard player," he explains. "They were married and had two kids. So, I was the nanny and the drum tech –all-round general gofer.

"I'm open-minded to trying different things. If someone asks: 'Will you come and help out with this?', then generally I will say: 'Yeah, I'll give that a go.'" That's an impressive attitude to life, Steven. "I don't know if it is wise or foolish?" he muses.

Robertson left Shetland at 21 to study drama at Fife College in Kirkcaldy and went on to hone his craft at Guildhall School Of Music And Drama in London.

READ MORE: Shetland star Neve McIntosh on genealogy, Doctor Who and childhood heroes

He has since racked up roles in BBC crime drama Luther, supernatural-themed comedy Being Human and sci-fi series Doctor Who, as well as ITV's Vera and The Bletchley Circle. His film appearances include Inside I'm Dancing, Joyeux Noel, Neds and T2 Trainspotting.

Away from work he is married to Charlotte – whom he met while at Guildhall – and the couple have a three-year-old daughter.

Shetland is now into a fourth series. Shooting the first scenes for the pilot episode back in 2012, did Robertson imagine the show would enjoy such success and longevity?

"I'll be honest, right at the back of my mind I had a good feeling about it," he says. "I wouldn't necessarily say that I was thinking we would have done our fourth series by 2018, but everybody involved wanted to make it happen.

"There was a great sense of adventure going up to Shetland and shooting it. The team always had a very positive energy behind it. Although a little part of me never dared to say it out loud, secretly I thought that it had a chance to go on and do well."

The latest instalment centres on an apparent miscarriage of justice. Local man Thomas Malone (Stephen Walters) has spent 23 years in prison for the murder of a teenage girl. With his conviction quashed, Malone is released on appeal and returns to Shetland.

Within 24 hours, the body of another young woman is discovered in uncannily similar circumstances to the original killing, leading many within the close-knit island community to point the finger at Malone.

As the 1993 case is re-opened and a new murder inquiry launched, Sandy (Robertson) is part of the investigation team alongside DI Jimmy Perez (Douglas Henshall) and DS Alison "Tosh" McIntosh (Alison O'Donnell). The stellar cast also includes Neve McIntosh, Mark Bonnar and Julie Graham.

Robertson plays the affable Sandy with such pitch-perfect verve that it is difficult to imagine anyone else in the role. Many years before Ann Cleeves's characters were brought to life on television, there was a radio adaptation in which Robertson played Perez.

What does he make of Henshall's on-screen portrayal of the DI? "Oh yeah, he is brilliant. As I always remind Dougie I could never have played Perez on the TV – I'm far too young," he laughs. "I've only said that to him once as a joke. That is my gag.

"One of the great strengths of Perez as a character is that he goes away and distils all the information in his head. It reminds me of John Thaw playing Inspector Morse."

Or Peter Falk as Columbo? "Yes, exactly. You can see that Perez is constantly working it all out. He has an awful lot of strands that he must figure out. It is almost like there's this mad, mathematical calculation in his head and it is missing one or two of the numbers.

"Perez knows where they should go, but he hasn't got the piece of information yet. Then it is always the surprise piece of information that changes the calculations. Dougie does that brilliantly. He is the right man for Perez in my opinion."

READ MORE: Shetland star Neve McIntosh on genealogy, Doctor Who and childhood heroes

While Robertson clearly adores the role of Sandy, he alludes to feeling a weight of expectation. "There are much harder industries in the world, but this can still bring its own stresses because you want to get it right, especially when it is representing somewhere that you came from yourself."

When he gets a break from filming, what is first on the to-do list? "I'm lucky to say that very much all my family are in Shetland," he says. "I still have a great number of friends in Shetland. Like a lot of island communities your family are your friends, and your friends are your family.

"Even if we are filming in Shetland for weeks and weeks, I still run out of opportunities to visit everybody that I want to and do everything that I mean to do when I'm home. But I certainly get back to the area of Shetland that I grew up in, Lunnasting.

"I always need to get back there as soon as possible just to see it; there are certain beaches and hills I need to look at. If you grow up with that scenery around you, I don't think it ever leaves you."

Shetland is frequently shot in and around his familiar haunts. "In series two we filmed on my aunt and uncle's farm on Muckle Roe," he says. "That was really surreal. It felt like art imitating life. I thought it was very brave of them to let a film crew use the farm, but they seemed to really enjoy it."

Many of the locals have played extras or been employed to help with production duties such as transport. As the only main cast member from Shetland, has that given Robertson a special kudos? "Ah, I don't know about that," he laughs, sounding instantly bashful.

The actor acknowledges some parallels with his on-screen alter ego. "There's always a sense with Sandy in the scripts that he has never really been away," he says. "Perez spent a long time in Glasgow and Tosh moved up from mainland Scotland, so Sandy is the local continuity.

"He is the local boy and knows people. Sandy is the local knowledge. That is a great crossover for me because when we are filming the Shetland-based scenes, I feel like I am Sandy."

What aspects does he most relate to? "Being the local guy and very protective of the local community. Perhaps having a different take on things which have happened in the past because they were a bit more personal to him – that is something which is big in this new series.

READ MORE: Shetland star Neve McIntosh on genealogy, Doctor Who and childhood heroes

"That element of him I can completely understand because whenever we go back to film it is my home. I am very emotionally attached to Shetland.

"People back home don't treat me any different. And nor should they. I would be mortified if they did. I'm Steven from Lunnasting and I hope to be no more or no less than that for the rest of my life. I would be perfectly happy with that."

Shetland returns to BBC One on Tuesday (February 13), 9pm