The Couch Surfer: 'On the Fourth Plinth, I meditate on my place in the world – and in art'

Tim Walker: Let's face it, I'm no Angel of the North

Trafalgar Square, dusk. As the sun drops behind Canada House, its dying rays climb Nelson's Column before drifting away into a darkening sky.

Traffic noise and the whisper of water from the fountains combine to produce an unexpectedly calming hum. From my perch on the plinth, six-and-a-half metres above the pavement, I meditate quietly on my place in the world – specifically, on my new role as a piece of conceptual art. Then a loud voice cuts through the balmy evening air: "Oi, mate! Give us a song!"

A couple of months ago, on a whim (perhaps a foolish one) I applied for a slot on the Fourth Plinth as part of Anthony Gormley's public art piece, One and Other. If you're not already familiar with the project, it entails 2,400 members of the public, over 100 days, spending an hour each on the 4.2 by 1.5-metre summit at the square's north-west corner. Sure, I like to show off as much as the next journalist, but mainly I just wanted to be involved. I still haven't decided whether Gormley's latest creation is "good" or "bad" art – let's face it, I'm no Angel of the North – but I can confirm that it's definitely art.

The application process was scarily simple; you can even complete it while drunk. I didn't have to explain my motives to the organisers. I didn't have to prove my cultural credentials. I didn't have to say what I was planning to do up there. (I did solicit ideas, by the way, but grew a little tired of pretending to be amused by the incessant suggestion that I should do it naked. The guy who stripped on the plinth two nights ago was taken away by the police. I don't plan to repeat that feat.)

I seriously considered doing nothing at all, a proposal met with uniform scorn and derision. Everyone seems to feel like they own One and Other – more so than other public artworks – and that its participants are therefore obliged to entertain them. Still, I wonder why we "plinthers" are expected to perform. Surely just turning up fulfils the brief? Nobody heckles Nelson, do they – and I don't see him doing his party piece.

Finally, a friend asked me a simple, searching question: "What are you good at? Do that." Well, I get paid to write, I thought. And I'm forever in search of something to knock together 750 words about. So here I am (below), on the plinth, writing this column – or, at least, an early draft of it. Oh, and for the sake of theatre, I'm doing it on a rickety old typewriter, dressed as something approximating an "old-school" hack: I have a press card in my hat, a pencil behind my ear, and a hip flask full of Scotch.

When I arrived an hour or so before my allotted time, I was asked by plinth organisers Artichoke to record an interview for an oral history of the project. The Wellcome Trust will collect and maintain the recordings, photos of the participants, and the 24/7 webcam footage of the plinth. Even after I've gone home, my hour will be archived for posterity.

There will be other online traces of the project, too, in #oneandother Twitter hashtags and plinther Facebook groups. At least one blogger is maintaining a personal record of the full 100 days, and I'm not the first journalist up here; this afternoon somebody broadcast their radio show from the plinth.

As the sun sets, my lofty platform is illuminated by floodlights. While, in daylight, I was just another bit of activity in a busy square, now I feel like the focal point. At about 8.45pm, I get caught in a somewhat stilted conversation with a group of teenagers down below, who persuade me to throw them a sheet of paper with their names – "Claudia and Sammy 4Eva!" – typed on it.

Some people are easy to please. Others less so. My assorted heckles include: "Do something interesting!" (heckle something interesting, then I'll consider it); "Take it off!" (see my comments on nudity, above); and "What are you writing about?!" (I'm writing about you...)

Who is One and Other for? The one on the plinth, or the others – in the square, on the web, in the future? Try as I might to concentrate on what I'm writing, I can't avoid becoming an interactive artwork, one that is purely public: of the people, by the people, for the people... Hmm. I think all this attention's going to my head, which means it's probably a good time to descend. One and Other is more than just the fellow sitting up here on this little concrete rectangle. My hecklers are a part of it, too – much as I'd prefer them to keep it down.