Dermot O'Leary: Michael Parkinson's little brother

Who is he? He comes in here all the time but I can't place him," says the waitress in the trendily down to earth north-west London café where I have just met Dermot O'Leary over coffee and French toast. In spite of his ubiquity - he has his own Radio 2 show on Saturday afternoons, is the face of Channel 4's Big Brother's Little Brother and makes regular appearances on the BBC - O'Leary is friendly and unassuming in the flesh.

Who is he? He comes in here all the time but I can't place him," says the waitress in the trendily down to earth north-west London café where I have just met Dermot O'Leary over coffee and French toast. In spite of his ubiquity - he has his own Radio 2 show on Saturday afternoons, is the face of Channel 4's Big Brother's Little Brother and makes regular appearances on the BBC - O'Leary is friendly and unassuming in the flesh.

It is this lack of airs that has helped to propel him within the space of a decade from lowly runner to the brink of the major league. Already a household name among Big Brother fans, the 31-year-old is playing a long game. He makes no secret of the fact that one day he would like to have his own chat show, but for now he is happy devoting his energies to a slightly incongruous portfolio that embraces Murfia, the production company he runs with television industry pals. Next week, Big Brother returns for its sixth annual outing and O'Leary will once again pop up nightly on television sets in Little Brother, the satellite show he has made his own. His job is to critique the reality TV saga from the viewers' perspective, mingling with fans who make the pilgrimage to the set and gossiping about the housemates' antics - the ultimate in water-cooler television.

The Catholic son of Irish parents, he has clearly given thought to the ethics of Big Brother. It is O'Leary who brings the subject up. "I really take issue with the whole argument of how exploitative it is. It's in the sixth series now - the contestants know what they're letting themselves in for. I know that the doomsday scenarios are spelt out for these people, and the checks they go through and the after-care that's there."

What about the infamous fight last summer, which earned Channel 4 a ticking off from media watchdog Ofcom? "No one was happy. No one was jumping around. The mood was very sombre and quite raw. No one wants to see people scrapping. At the end of the day, people have to be held accountable for their actions. If it had happened on Borehamwood high street, the police would have clipped a couple of ears and sent people home, but it happened on television."

He has little time for naysayers like John Humphrys, who laid into Big Brother in his McTaggart lecture at last year's Edinburgh Television Festival. "A guy that hasn't watched television for seven years shouldn't be telling people what they should and shouldn't watch. I despise that kind of snobbery. For me, you can get as much out of that show if you're a body language expert at Cambridge as you can if you are a mother or father trying to put their kids to bed while there's something on in the background."

He warms to his subject. "It doesn't annoy me that people don't like it. What annoys me is when people think that people who watch it are beneath them. How dare they presume to tell other people what they should and shouldn't be watching?"

Following a "very happy" upbringing in Colchester and a degree in media and politics, O'Leary spent 18 months in his early twenties as a runner: "The wages are shit, but that's all part and parcel of it. It teaches you humility." He eventually landed a job as a researcher on Channel 4's Light Lunch, where he graduated to become the warm-up act. When the channel's then embryonic youth strand E4 was scouting for new presenters, he got the gig.These days, he appeals to a very different constituency as Radio 2's youngest presenter. "This is the weirdest thing. I'm there, I presume, to bring the age of the listenership down. We did some research recently, and while the average audience for Radio 2 is 43, my average listener is 51, which made me scratch my head a little, but I'll take all comers. I don't think many people in their fifties particularly want to listen to the ramblings of a 31-year-old." He is thrilled to be working alongside his heroes Terry Wogan and Jonathan Ross: "You try desperately hard to play cool and inside your little heart's beating."

When he is not presenting live television or rambling on the radio, O'Leary is hard at work at his production company. Murfia's latest documentary, Generation Jedi, an authored film about the cultural phenomenon of Star Wars that goes out on BBC3 this week, gave O'Leary the perfect excuse to dress up in Jedi gear. The company has also produced a pilot for a new Channel 4 breakfast show. Instead of trying to recreate the glory days of The Big Breakfast, Murfia has come up with a graphics-based show called The Morning Mash. "It's a 15-minute précis of what happened yesterday in a very funny style. For example, every time we mention Charles Kennedy we superimpose him onto a picture of a pub and you can hear this boozer and people shouting: 'Come back, Charles.'"

If he were forced to choose, O'Leary would pick television over radio or production - "there's no feeling in the world like being on live TV". The medium is not, however, without its drawbacks. Shortly before the general election, O'Leary was branded a Labour luvvie after inadvertently suggesting at a Make Poverty History rally that Tony Blair should become head of state.

"I'd been out at an Athlete gig, absolutely plastered, and I turned up thinking I was hosting a question-and-answer session for first-time voters. The next thing I'm doing a satellite link with Bill Clinton when I can barely focus." When his fellow presenter, June Sarpong, told the audience: "I'm very excited because I have always wanted to say, 'It's my pleasure to introduce you, Mr President' and obviously we can't say that over here", O'Leary chipped in with a wisecracking "yet".

He is still cringing from presenting the Elle magazine style awards earlier this year. "It was the worst night of my life. I had this Homer Simpson moment on stage. My brain started talking to me and just went: 'Oh yeah, fashion and self-deprecation don't go that well together, do they?'"

O'Leary is prepared to wait a while before stepping into Michael Parkinson's shoes. "I'm 31. You've got to have lived a little before you have the right to do something like that. I'd like to give a chat show a shot, but my career is not going to be defined by whether I get that gig or not. As long as I'm working, I'm happy."

In the meantime, he believes the key to live presenting is being quick, confident and well-prepared. "If you prep, you can go on television and you're playing in a sand-pit. If you don't, you get shown up. When you go live, you're either king of the world or an absolute chump."