'No full frontals, but we might have to see a teensy bit of fluff'

Male pride is a curious thing. It is easily aroused and quickly deflated, and appealing to a man's physical vanity is the surest way to air-pump his self-regard. Sadie looked disarmingly innocent as she swan- necked her face over her wine glass: "You really would be doing me an enormous favour, since there isn't time to find a professional ... and, um, I need someone who's got just the right body," she added hastily, fluttering her fingers along my arm.

"OK, I'll do it," I slurred. "But no full-frontals," I growled, clumsily thumping my empty glass on the restaurant table. She mocked shock: "Of course not ... we might just have to see a teensy bit of fluff, but your face won't be seen at all."

And there it was: I had agreed to "perform" as the "nude" male model in the title sequence of her forthcoming television series on women's sexual fantasies.

It was a promise I dimly remembered when she rang the next morning to make arrangements for the film shoot. Her voice was brusquely efficient: "Don't wear any tight clothing. We don't want any panty-lines showing." Distant alarm bells began to ring. "If anything starts moving down, um, there, just hum the theme tune to Match of the Day. It always works. Don't let me down."

Small beads of anxiety pearled in my hands as I stood in front of the bathroom mirror. She had wholly misjudged my physique. I engaged in a frantic set of exercises designed to achieve Gladiator-sized bulges in less than 20 minutes. Breathless and giddy, I dived into the shower and scrubbed every cell of my body's surface. Underwear flew out of my drawer as I searched for the inscribed posing pouch an ex had archly bought in Amsterdam years ago. It was to be the ultimate line of defence underneath a capacious pair of boxer shorts. What would the professional female model, whose hands and body would be caressing my own, be expecting? Emerging from the house with brushed-raw gums and stinging with aftershave, I took a train to south-east London.

"Just rub it on a bit," the porcine director wheezed as he sprayed my shivering body with baby oil. The model, a miniature Michelle Pfeiffer with black hair, was nonchalantly gluing red fingernails into place. I was made to pose in artful positions, chest puffed out, as her talons raked various parts of my tensed body, the camera suggestively following them to their path's end underneath the band of my boxers. I winced as a nail hoed a clutch of chest hairs from my skin.

It was her bright idea to get me to lie on my front, shorts pulled down to my knees, rear exposed, as she aimed, then lowered her breasts with pinpoint accuracy on to my buttocks. "Line up those cracks," the director enthused from behind the camera. "And let's see a bit more of the purple," he added. I pressed my hips to the cheap linoleum dais in horror, until I realised he was referring to the coloured backcloth behind us. I felt ridiculous. Match of the Day? Some hope.

The final humiliation was when the director decided that the title of the series should be written in lipstick across the front of my body. The camera hovered in coital proximity to my groin. The spelling of the word "Erogenous" caused a few problems, but before Lina could display her calligraphic skills, the cameraman nervously trimmed my lower stomach hair. "You've got to be shorn so we can really see it," he muttered. Oh, the shame of it.

I felt an odd sense of abandonment as I walked to the train: although I had, under the torching glare of the lights, begun to feel what those sad individuals - seemingly always travelling alone in the backwoods of America - are supposed to undergo at the spidery hands of investigative aliens, I was now just an ordinary person dressed in the shapeless mufti of everyday life. I realised that I had also felt a guilty sense of pleasure in exposing my body. A phrase I'd heard - "the undressed is vulgar - the nude is pure" - echoed through my mind. But isn't it all a matter of intention? Or do I mean "attention"?