I'm in the sparsely populated carriage of an Overground train. As we crawl into Euston, the realization that I'm the sole audience to a woman a few seats in front, tearfully berating a man on her mobile phone, tears me out of my reverie. ‘It's over,' she tells him through heaving sobs. ‘Don't you fucking talk to me. I fucking hate you. Why? Don't you fucking give me why, you stinking bastard. Don't pretend you don't know. Don't pretend, don't, don't you fucking pretend.

' All her murderous despair throbs in her thumb as she terminates the call. She leans her head against the window, still volubly crying. I gaze out the opposite side, heat creeping up my face. I tell myself I'm an involuntary witness to another's lack of emotional inhibition, conveniently passing over my own rapt interest in the scene. Several minutes later I'm hovering in front of the magazine racks in Smith's. I stare glassily at the covers of Heat, Closer, Reveal, the titles amplifying the promise of furtive proximity intimated in the hazy shots below. An arrow tagged Serious tummy! points to the slack flesh spilling over the bikini bottom of a soap actress hunched on the edge of a sun lounger. Another, aimed at the ribcage pressing through the skin of a bikini-clad TV presenter, asks Dangerously skinny?! Something about the distracted obliviousness of their postures and expressions seems more obscene than anything the dead-eyed glamour models nearby can conjure.

Too self-conscious to browse, I shuffle out, taking with me only my mild shame. These unexceptional few moments have revealed to me my participation, at once resentful and willing, in a culture of intrusion, held together by the unholy alliance of voyeurism and exhibitionism. The first principle of this culture, upheld by wire taps and telephoto lenses on the one hand and by the pervasive casual display of personal intimacies on the other, is that I should know everything. Nothing, from the near side to the furthest reaches of bodily and emotional experience, should be kept from view. As those few minutes showed me, it's hard to opt out of this culture and the malevolent excitement it stirs up. Many celebrities and other public figures rightly protest against this culture, but their lamentations for their lost privacy only feed the spectacle they want to escape. Nothing seems better calculated to provoke an assault on privacy than the plea to respect it. What accounts for this relentless war on our own and others' privacy? What, exactly, are we attacking?.