He sits opposite me on an elaborate couch. We are in a suite at the Gritti Palace in Venice overlooking the Grand Canal, the Salute and ranks of bobbing, glossy, coffin-like gondolas. It is a ponderous, baroque room with heavy brocade curtains and a thickly patterned carpet. The air seems greenish, dusty and unnaturally still. It is an ominous enclave in the midst of this city's endless beauty. It is a good room for a death. Soon after we start to speak, Allen abandons the couch. He has grown deaf — "one of my only flaws" — and he can't hear me. He sits, instead, at my right hand and so we talk, crouched over my recorders. In the dim light we must appear to be conducting a seance.

His shift of position means I can now see his skin clearly, and it is, indeed, strange. It is stretched, pale and startlingly flawless, over the bones of his face. It is not exactly young skin, but it is not old skin either. It looks, somehow, unreal.

I am told he is very fussy about his health, so perhaps this off-white membrane is generated by some exotic dietary and exercise regime. Like many Americans, he probably thinks death is optional and eternal life is just a matter of the right combination of pills and food. So, I ask him, if offered an immortality pill, would he take it?

"Errrrrrr, I'd want to think about it a little. But I probably would take it because you know the problem of the concept of forever is that it's a human concept, there isn't going to be a forever to get an apartment in. After a while, sooner or later, even if you live the duration of the existence of all that exists, there won't be anything else, nowhere to go. I've often thought that if you say you could be immortal all of a sudden, you'd be very careful about what you ate and where you walk. The odds are mathematically that eventually you'd get hit by a car."

This does not quite make sense but the speech pattern is instantly familiar. It is every Woody Allen character he's ever filmed, whether played by himself or not, except there are fewer jokes. Occasionally, he makes himself laugh — an introspective stutter — but, otherwise, he seems deadly serious. He is so like the filmed "Woody Allen" the effect is disturbing. Stripped of its comic intentions, the famously neurotic monologue becomes perversely funny. I find myself thinking he must be joking. Surely, nobody can be that self-involved. But he is, and I can't stop myself laughing. He doesn't seem to mind, or perhaps he doesn't notice.

Anyway, let's discuss death, the real subject of this article. Allen has spent years in psychoanalysis but he seems to have discovered the true root of his problems unaided.

"I have my own theory about my melancholia. I was a very sweet and happy kid until about five, then suddenly I turned sour, into a pill. But nothing traumatic ever occurred. My parents lived to be a hundred and they were good to me, nobody beat me, nobody abused me, nobody molested me. I had toys, they gave me food and shelter.

"I think I became aware of my mortality at that age. It was then I realised the situation we are in. It so traumatised me that, from that day on, I could never look at the world again except through a bleak prism which I find reality and which other people find pessimism, misanthropy, cynicism. I don't say it's any of those things, I think I'm completely realistic."

Coughing to cover my laughter, I suggest he is suffering from a bad case of seriously arrested development.

"Yeah, I feel something happened there and I'm 70 next December, and I've yet to see or learn anything that has not confirmed my worst fears. Mark Twain thought the more you learn the worse things got. That's how I've felt. And, my God, I'm right. With the emerging knowledge of quantum physicists, things look worse than ever. Everything sprung into being with no point, haphazardly and with no design, and will eventually be gone. No air, no light, nothing at all."

Stricken by this insight, Allen has, since the age of five, been obliged to seek distractions. He is no good at sitting and thinking because he always thinks the same miserable thing and, without distractions, he fears he will grab people in the street and tell them they are going to die. He says he needs a newspaper if he gets in a lift. An eight-floor ride without reading matter can be intolerable. His main distractions have been stand-up comedy, jazz and film-making. But they could be anything. Everybody, whatever they do, is just distracting themselves all the time.

"I had a line in one of my movies — 'Everyone knows the same truth.' Our lives consist of how we choose to distort it. One person will distort it with a kind of wishful thinking like religion, someone else will distort it by thinking political solutions are going to do something, someone else will think a life of sensuality is going to do it, someone else will think art transcends. Art for me has always been the Catholicism of the intellectuals. There is no afterlife for the Catholics really, and there's no afterlife for the arts. 'Your painting lived on after you' — well, that doesn't really do it. That's not what you want. Even if your painting does have some longevity, eventually that's going to go. There won't be any works of Shakespeare or Beethoven, or any theatre to see them in, or air or light. I've always felt you've got to live your life within the context of this worst-case scenario. Which is true; the worst-case scenario is here."