"You're sitting in the director's chair," mutters Marcus Lush as he sidles into the TVNZ boardroom. I didn't notice, but it's soon clear that Lush, who's up from Bluff for the week, would rather be calling the shots.

It's obvious this interview is something of an ordeal, or at least a pain in the butt for Lush, to be endured for the sake of publicity for his new TV series South, and Radio Live's breakfast show. He's been known to walk out of interviews and when I ask a question, he fixes me with a steely stare as an uneasy pause clocks up 8, 9, 10 seconds.

Surely, at 44 years of age, he must know this is disconcerting, even if he doesn't care. People have called Lush idiosyncratic, eccentric, even odd, but that's part of his charm. Part of his success. In the early 90s, long before the Russell Crowe film, Paul Holmes made mention of Lush's "beautiful mind."

Getting his break in student radio at bFM before moving to talkback, this long-anointed successor to the radio-king throne has been credited with concocting a unique style of broadcasting: a mellifluous flow of ad hoc tangents, irreverence, unusual details and dry witticisms. With his "brilliants" and "hooroos" and his empathy with the common people, Lush strikes an easy rapport with listeners.

It's a touch that saw him snatch the title of Best Talk or Current Affairs Host at the 2007 New Zealand Radio Awards from the hands of Holmes. His career has tracked along nicely TV-wise too, since his offbeat beginnings on TV2's mid-90s news-lite show Newsnight.

But TV has become more than just his bit on the side as he's conquered the small screen with doco-style travel shows including Intrepid Journeys, Off The Rails (journeying along New Zealand's railway lines), Ice in Antarctica and now South.

With plenty of the fieldwork he loves, these shows seem a direction more suited to Lush. His informal style, left-field humour and ability to make small observations interesting is largely why Off the Rails was 2005's second-highest rating show (after Dancing With The Stars) and batted well above its weight with DVD and overseas sales.

The gig won Lush the best presenter prize at the 2006 Air New Zealand Screen Awards, and best documentary. Yes, he's surprised at the success of a show some saw as hardly commercial. "But it wasn't about trains, it was about New Zealand," he says.

He came up with the concepts for both Off the Rails and South. "A lot of people come to me with proposals for shows to make, but I can only make stuff I'm interested in, and my interests are quite narrow."

In person, Lush isn't as well-filtered as he is onscreen. Funny, but diffident. Standoffish. Awkward. Eccentric. Slightly patronising. Is this a cultivated persona, or can he just not be bothered trying to be something he's not? There's a journalist's conceit that you can spend an hour with a person and profess to have psychoanalysed them. Mostly you pull it off, because people have a narrative that you see or see through.

Marcus Lush isn't one of these people. He's enigmatic and content to remain so. There's a word overused by Generation Y to the point of banality, and that's "random." Marcus Lush is random, especially during a tangent about New Zealand's alleged fascination with elephants.

At times he shrugs off the cloak of diffidence and is frank and self-aware. Sometimes he even slips into a confiding tone, but then he'll suddenly snap at you. Still, despite or perhaps enabled by those pauses, you sense he's trying to answer each question honestly and eloquently.

Certainly he's not shy speaking his mind. He's outspoken on everything from Antarctica ("I think there's probably no reason for Scott Base: it's a club") to those who grew up wanting to be on the radio ("the world's most annoying people") to the Off The Rails-caused misconception that he loves trains, which led to him being asked to help save that "ghastly train" – the Overlander. "Rail's done its dash."

It'd be hard to host talkback without being opinionated. He still seems slightly surprised that he got a national gig based in Bluff, at first doing Radio Live's night-time talkback from Invercargill (which he also considers home). And yes, he thinks talkback has helped tune him into the Kiwi psyche. "When you're getting people who are almost like a flock of birds flying in formation, talkback can be the most wonderful thing. But if you're talking about the death penalty or banning dogs I can't stand it – I don't find it a safe place to be always."

Lush, who relishes radio's efficiency, immediacy and challenge, traded talkback for the station's breakfast-host gig in May 2007. While he says the show is still evolving, the move to mornings has been a welcome one: partly because the harder-news, interview-heavy style is a challenge, and partly because it frees up the rest of the day without the spectre of work looming. "[But] you can't go out late at night and you never really get a lot of sleep."

He gets up at 4am, drives 20 minutes from Bluff to the Invercargill studio, and does some prep before the 6am start. This year, though he'd rather not, he's circumspect about doing most of his shows from Auckland. Typically, Lush doesn't insist on a hotel; he dosses with friends. Some commentators have said he's better at TV than radio; better at talkback than hard news.

Lush, who says he doesn't read his own internet-bound press, is scathing of "google journalism", although he admits he's googled himself (there's 6000-plus hits by my tally). "Fortunately a lot of the things I've done people have said nice things about." He's not without ego, but the absence of false modesty is refreshing. However, he doesn't think he's invented a new broadcasting style. "If you're lucky you can put away the nerves and be yourself."

Nerves also crop up in rarely given interviews. "Out of the whole TV-making process, probably to promote a show and do interviews would be one of the more difficult things. Because I don't always know what the right and wrong answer is." He's concerned by a gap between the person he is and what appears in print. "You leave to wash your hands and they say obsessive-compulsive." After a protracted pause, he admits that he has had "a fright with the press."

He became wary of journalists after they jumped all over him after he was admitted to Hanmer Springs in 1998 after a battle with the booze.

Unfortunately, his last name was too tempting a headline for sub-editors. Although Lush appears not to care what people think of him, he does. "I'm incredibly thin-skinned. I think all broadcasters are – well, not incredibly thin-skinned but it's also a ratings game – you're judged by how well you're doing, [by] whether people like you or not."

Is he ambitious? "No, God, I want to give it all up!" Really? "Oh, f**k yes. I can't stand it! I've got no ambition in the world. I'm the accidental broadcaster. I went down to Invercargill to give it all up. I just want to paint or carve or garden ... I don't want to be Brian Turner but I want to be someone who just has an incredibly simple life. Someone with high spiritual goals."

But if he sincerely wants to give it up, surely he could. "Oh, it's easy to say this would be an enjoyable job for a while, or I'm lucky to have this opportunity, so part of you feels churlish for not doing it. But look, I've got a million things I want to do." And he'll be doing them from Bluff.

Living in our southernmost town for seven-and-a-half years has gone beyond being eccentric. Auckland's no longer his home. "I'd just spent a lot of time there, there were a few ghosts, and I decided it was time to leave."

Craving life in a compact community by the sea, he considered many towns before sticking the pin in 1800-strong Bluff. "Moving there was the most significant thing I've ever done. I believe I was called to Southland – it was something I couldn't resist. I don't know why, I just love it."

Get him talking about the Deep South (locals counter that detested term, he says, with The Shallow North) and there's no mistaking the passion, honesty and captivation in his voice. He can rabbit on about the unique characters, stories, history and geology without any pauses. And that's the bones of South; seven weeks' circumnavigating the south of the South Island squeezed into seven half-hour episodes.

Even if he warns us to buckle ourselves in for the ride a few too many times, it's a journey well worth taking. The often-remote spots are breathtakingly beautiful, then there's the classic characters: modern-day Burt Munros with strange passions such as making a garden out of buoys. "There were stories that were just desperate to be told."

We hear about an angry dad who (rumour has it) threw the man who knocked up his daughter down Dog Island Lighthouse, and get-rich schemes that bankrupted whole towns. The depth of Lush's research is clear. "So much TV seems to be a big-city person's look at small towns and slightly belittling, as if small-town people are playing with half a deck. I was determined it wouldn't have that whimsical nostalgia look."

Cleverly interwoven are archival footage, offbeat quips and unexpected anecdotes. And if you want to see Lush shirtless in a tepee, or swimming in his gruts in a river, here's your chance. Lush, who usually looks like he's ransacked an opshop after the cool kids got there, hasn't had his signature scruffy look with his five o'clock shadow and dishevelled hair tidied for the camera.

South also peeks into his old-school 1960s-style home with its formica table, stacks of books and railway cups. There's currently a vacancy in the girlfriend department ("I'm not having three-in-the-bed romps or anything") but he's made long-lasting friendships with doughty Southlanders, after some initial sizing-up. "People are quite cagey and I like that because I'm quite cagey."

The madcap mates are always "up to adventures": canoeing trips, expeditions to historic sites, searching for shipwrecks, collecting paua. "It's a bit like Last of the Summer Wine. Outdoors stuff that you miss out on growing up in Auckland: whitebaiting, hunting, fishing. It's taken me a long time to find people that are into it."

He does miss the odd thing about Auckland. Not friendships – they've dwindled and been replaced, but the art galleries, kauri trees, West Coast beaches, volcanic cones, a different shade of green. "And DressMart. I'm trying to organise trips for Southlanders to come up to DressMart. There's one in Christchurch but it's not as good."

Down south, people are more likely to see Marcus the local rather than Marcus the broadcaster. "It's more anonymous for me, people are more respectful." Though not always. Once a family with train-mad kids turned up at his house. "Dreadfully behaved kids as well. I think 'for f**k's sake, it's TV, not an open invitation to come round'."

It's nice, he says unconvincingly, that people think he's approachable. "But I'm not that approachable." Certainly, there's a smudge of the curmudgeon in South, especially when he moans about the young "van bludgers" who "treat New Zealand like a cheap date."

There's talk of more series covering the country and (perhaps in jest) of three nascent books including autobiography Picnic For One. "It's a good title eh? I thought it summed me up."

* South premieres tonight on TV One at 7. The Marcus Lush Breakfast Show airs weekdays 6-9am on Radio Live, 101.6 FM.