Who is Aidan Turner? Well, sometimes he's a DJ who works as a doctor's receptionist, sometimes he's a pre-Raphaelite genius and libertine, and sometimes he's a 100-year-old vampire who's kicked the blood-habit and is sharing a flat with a werewolf and ghost. (Sometimes he's other people but that's in plays and I only watch the telly.) Okay, Aidan Turner is a tall, dark and handsome actor from Tallaght, who you may recognise from The Clinic, who's currently appearing in BBC3's supernatural drama/comedy Being Human and is soon to star as
19th century painter Dante Gabriel Rossetti in BBC2's historical drama Desperate Romantics. ("It's already being described as Entourage with easels," he says with a groan.)

So how did one of "us" end up working so prolifically for one of "them"? Being Human was originally made for BBC3 as a once-off pilot starring a completely different set of actors, and when it was commissioned as a six-part drama series they decided to recast it. So out went Angela Riseborough and Guy Flanagan and in came Lenora Crichlow as a friendly ghost, and our own Aidan Turner as a vampire called Mitchell who's trying to be good. (The only actor remaining from the original cast was Russell Tovey as Mitchell's uptight werewolf flatmate.)

"I got a call from my agent telling me about the project: a ghost, a vampire and a werewolf sharing a flat in Bristol," explains Turner. "I was convinced it was a comedy and she was convinced it was a drama. It turns out it was somewhere between the two. I met the producer and I met the director; I had a good meeting, went on holidays. Then they called me back towards the end of the holiday and flew me back to meet me one more time and I got it.

"The funny thing is, when the idea was conceived, Toby Whithouse thought of the character as Irish for no other reason than he wanted to have an Irish vampire. Maybe subconsciously when I went into the meeting it triggered something in his head and worked in my favour."

Being Human is great television: a sitcom premise that develops into a spooky, witty and much bigger story about conspiracy, addiction and denial. It's dark. "And it's going to get darker by the end," Turner promises gleefully.

The news that he had got the job came at a pretty good time: the day he and his actress girlfriend Charlene McKenna (who starred in Raw, Pure Mule, and Single Handed) moved to London pursuing interesting acting opportunities. ("Without the safety net of an actual job," he notes.) Why the move?

"Ireland's fantastic and I've worked almost non-stop here for the past four and a half years with the Abbey theatre and various other companies," he says. "But it's not enough to keep you going all the time and what every actor wants to do is to work. People say it's brave to make the move, but I think it's braver to stay put. Acting's such a weird job. You're on top of the world one week and the next you've no work and still have the mortgage or the rent to pay.

"The fact Charlene and I are both actors means we can help each other in all kinds of ways. It can be frustrating sometimes when one of us isn't working, or when someone doesn't get a part they really want and the other does, but we're both adults and we can deal with those situations, so it's usually more of a help."

Turner fell into acting almost by a process of elimination. "I'd just finished my leaving cert and didn't know what I wanted to do," he says. "I've a cousin who's an actor so following that path wasn't as farfetched as it might have been for other people and it seemed like fun. I did ballroom and Latin American dancing for about 10 years; I even represented Ireland. So I did have a flair for the creative side. Then I got into the Gaiety school of acting and suddenly from then it all just came together."

Turner seems like an enterprising sort, landing theatre job after theatre job and appearing in The Clinic before moving to London and landing two high-profile BBC shows within two months. "Well, the second one wasn't that difficult," he admits. "When you do a read-through for the BBC everyone's there, all the top execs. And they'd been looking for this character for Desperate Romantics for weeks so they asked me to send off a tape. So I got Russell [Tovey] to shoot me on a little handycam doing a scene. The bloody camera was shaking and it was a complete disaster. [He is a werewolf.] But we sent it off and a couple of weeks later I got the part."

Desperate Romantics is loosely based on a non-fiction book by Franny Moyle about the 19th century Pre-Raphaelite Brotherhood which featured the artistic geniuses of their day – Gabriel Rossetti, James Collinson, John Everett Millais and William Holman Hunt. Turner plays the womanising sensation-hunting poet and painter Rossetti, alongside some top British acting talent including Tom Hollander and Zoe Tapper.

"We've stuck incredibly close to history although we've condensed the timeline," says Turner. "We've put 15 years of their real lives into two or three years, but everything that happened in the scripts happened in the real lives of these guys, and Rossetti's a great part to play. He was an absolute chancer and womaniser and a big drinker and drug addict. Every negative connotation you can attach to somebody Rossetti was probably it. But wrapped up in all those negative things he brought the brotherhood together and he was an incredibly charismatic and charming guy who bedded a lot of the women he painted. Everyone loved him."

It sounds glamorous. "Oh yes, getting up at 5.30 this morning when London is covered in snow and all other productions have been stopped," he says and starts to laugh. "That's very glamorous. Wearing 19th century costumes in a freezing studio, and those costumes do not keep in the heat, and when you look around all the crew are kitted out in one-piece North Face suits and they're roasting next to massive heaters – that's very glamorous."

So he's going to rethink it all and do something else?

"Get a real job?" he says. "I've no idea what I'd do. Acting was already a default for me. I wasn't born to be an actor. It's that there's nothing else I could do. What else would I do? I'd probably move and take up surfing. Go to Australia and try teaching it."

That's not a real job either, I tell him.

"Yeah, I know," he sighs, before adding: "I love acting. I don't want to get a real job." And he says it in a vaguely nervous voice like I might just make him apply for one.