His hair is so tousled that one could be forgiven for thinking he has come straight from a few bouts of wrestling. The look isn't improved by a less-than-fresh white T-shirt, which he is wearing inside-out, as if to hide the stains of yesterday.
Worry not, however. The actor, who played vicious soap villain Trevor Morgan in EastEnders and was most recently seen on the Scottish stage as Johnny Byrne in The Hard Man (the quasi-autobiographical play that Jimmy Boyle wrote with Tom McGrath), has not suffered a catastrophic decline in his personal fortunes. Rather, he's come straight from the rehearsal room, where his rough and ready appearance is a facet of his role.
Never afraid to tackle characters who adhere to a dubious form of machismo, Ferns is playing Lee - a violent, heavy-drinking criminal - in American dramatist Sam Shepard's acclaimed 1980 play, True West. So what is it that attracts the actor to such roles?
"It's basically the fragility of masculinity," he says of the character, who arrives in his mother's South California home to find his brother, movie screenwriter Austin, crippled with writer's block. What ensues, via interactions with Hollywood producer Saul Kimmer, is a fascinating exploration of masculinity through two very different brothers whose personalities begin, rapidly and disconcertingly, to merge and criss-cross.
"With Lee, a mask is put on, so that no-one can question me and no-one can touch me," Ferns explains. "I don't let anyone see through my mask, and woe betide anyone who starts to crack it open."
Characters such as Lee - whose ultra-machismo points towards a more complex personal reality - tend to come Ferns's way. The actor can see why director Phillip Breen, who staged The Hard Man in 2011 and is directing True West at the Citz, wanted him to play Lee, following his critically acclaimed portrayal of Johnny Byrne two years ago. There are, Ferns observes, interesting similarities between the two characters.
"Lee's put the mask of the cowboy on so that no-one can see how much pain he's in underneath. I think it was the same with Jimmy Boyle. What interested me with The Hard Man was the question of why someone would do things like that. I know personal circumstances have a lot to do with it; needs must, you do what you have to do. But there's something about the savagery of the things that he did and the way that he went about them. The first question I had was, 'What was he hiding?' I wanted to know what was underneath that brutality. It's all, basically, fear."
Inhabiting characters who are driven by fear, and by the need to hide that fear behind a shield of overwrought, often violent masculinity, is clearly a great attraction for Ferns. He talks passionately and enthusiastically about acting which for him starts not from analysis, but from emotion.
"I don't approach plays in an intellectual way," he says. "I'm just a visceral actor, I go with what my instincts tell me. Both with The Hard Man and with True West, it's about finding something visceral. Within each of us [men] there's that kind of savage male identity. Particularly if you've got a family. You'd do anything for them, you'd die for them."
If True West is a powerful and intriguing play about masculinity, it is also very much about that masculinity as conceived in an American context. Lee and Austin's absent father is a washed-up, alcoholic bankrupt who has taken refuge in the desert of the southern United States. Their mother is an unlikely, almost-1950s image of American femininity.
There is in this, says Ferns, a radical hyper-realism and a profound challenge to the dominant American self-image which is reminiscent of the films of David Lynch. In fact, Breen has been showing his actors scenes from Blue Velvet as part of the rehearsal process.
"Sam Shepard can see through [the myth of the American male]," the actor suggests. "So does David Lynch; he can see right through America. Look at Blue Velvet. You have the white picket fence, the beautiful house and the fire engine going past with the firemen waving, but underneath all that there's corruption and violence. There's sex, but it's sex linked with violence. True West is similar. There's a lot of frustrated sexuality in this play."
For Ferns, the Shepard/Lynch comparison holds up particularly strongly when it comes to the issue of the Hollywood pastiche. Whereas Lynch is famous for his extraordinary twisting of many cinematic genres, ranging from the American teen movie to the noir thriller, True West, as its title suggests, is a bleakly comic take-off of the Western.
"This entire play is a parody of the traditional Western," the actor contends. "Instead of the classic gunfight, you have a golf match. Instead of sitting by a campfire, Austin's sitting at typewriter by candlelight; the only way he can feel inspired to write is to try to recreate what the forefathers had, in terms of candlelight, the cabins, the wilderness. But he's in a suburb, 40 miles from Los Angeles. There are cars going past and kids screaming in the street. That's what I mean by saying Shepard saw right through these constructed notions of America."
There's a surreal, almost dream-like quality to Shepard's writing which leads Breen and his cast to view the outward realism of True West with more than a little scepticism. "I'm not sure any of it's real," says Ferns. "The way we're looking at the poetry of it, Lee is a creation of Austin's imagination."
That certainly tallies with Shepard's own observation that he "just wanted to give a taste of what it feels like to be two-sided. It's a real thing, double nature. I think we're split in a much more devastating way than psychology can ever reveal. It's not so cute. Not some little thing we can get over. It's something we've got to live with."
Translated through Shepard's remarkable imagination, that duality has wild theatrical possibilities which Ferns thinks will go down particularly well at the Citizens. "I'm looking forward to doing the play in Glasgow," he comments. "I'll tell you something now, without giving too much away: it's madness and mayhem in the second half of the play. If the rehearsals are anything to go by, it's going to be interesting. If you stick to the text as written, the comedy comes out, because it's a very, very funny play."
There is, the actor suggests, something in the Glasgow theatre audience, in its energy and social diversity, that makes it particularly ripe for Shepard's drama. "I think the Glasgow theatre audience is great, because it comes from all walks of life. That's a big deal, because in London it's not like that. In the West End it's tourists or the person who doesn't think twice about spending 80 quid on a ticket. Whereas, when I did The Hard Man at the King's in Glasgow, there were people from every kind of background, and lots of working-class people."
Given Breen's past successes in Scotland - including The Hard Man and his 2008 Citz production of Harold Pinter's The Caretaker - audiences can be confident that the work is in good hands. "When he does a play, he lives and breathes it for that time," says Ferns. "I think he's bereft when it ends."
As if that weren't reason enough for the Citz audience to embrace True West, there is also the matter of Glasgow's continued fascination with country & western music. "Glasgow and the West of Scotland have that link to Westerns and country & western culture," Ferns observes. "There's the Grand Ole Opry; my Mum used to take me there when I was a kid. The way I see it, Glasgow audiences are going to love this. They're going to see so much in it they can relate to."
True West is at the Citizens Theatre, Glasgow, from October 29 to November 16. For further information, visit citz.co.uk