Six weeks ago, I went to a party at a policewoman's house. She works in the incident room at New Scotland Yard and, over a bucket of booze and a mountain of cigarettes, she talked of gun crime, drugs and the war on terror. Then she dropped a firework.

"We have a bestiality incident recorded every day, you know," she told me. "Every single day."

I went home stunned. Who are these people? Do they rape fish? Rabbits? Is it consensual? (Is it fun?)

I went to the Apollo Theatre on Shaftesbury Avenue in London to see Edward Albee's play The Goat. Jonathan Pryce, as Martin, an architect, declaimed his love for a goat named Sylvia. "Yes, I'm screwing her," he tells his wife. "I'm seeing her and we are having an affair. She is my first. She is my only." His wife cuts Sylvia's throat.

I tracked Albee down to his hotel. His play is not so much about bestiality as the prison of sexual convention, he says. But, he insists, many of his colleagues on the faculty at Houston University have had sex with animals. He asks me: "Have you ever looked into the eyes of a goat close up? They are very beautiful." No, I haven't. I don't like the smell. I like my animals dead on a plate with vegetables.

Albee pauses, then continues. "Bestiality happens with a greater degree of frequency than we are prepared to realise. Women usually do it with dogs and horses, and men do it with a wider variety - pigs, sheep and even geese."

I decide to surf some websites. A woman fellating an Alsatian (dog). Then a donkey. Next a horse. In the missionary position with a snake. Another dog. A man and a chicken. With further surfing, I learn that animal sex shows occur in many countries. There is, apparently, a reindeer sex show in Norway, and, in South America, a porn circus featuring llamas. Watching a woman being mounted by a dog is considered the ultimate stag party in Japan. There are piles of videos and magazines, and a festival in South America.

There is a bitter schism within the bestiality community, I learn from Understanding Bestiality and Zoophilia, a tome by an Israeli academic, Hani Miletski. There are the more numerous bestialists, who are rather sluttish. They are sadomasochistic, curious or exhibitionistic, full of ennui, or doing it for the money. They are responsible for the pornography and the sex shows. Zoophiles, however, feel married to their animal lovers. They are romantic and secretive. Albee's hero, Martin - "I love her!" - is a zoophile.

Miletski set a questionnaire for zoo-philes, and discovered that they hate bestialists. One respondent said: "Bestialists use the animal for sex relief. It's a sex toy. A zoophile relationship is more. It's a marriage." An Arkansas zoophile told her: "It's a worse commitment than marriage because you can't walk away. They don't understand if you leave them."

Since the birth of the World Wide Web, zoophiles have organised themselves into online groups, such as Advent Partners, Stasya's web page and Furry MUCK. One zoophile says, "We come from every walk of life." Another opines: "There are as many women as men, but they keep quiet about it."

Some zoophiles consider their true spirits to be animals, and their human form a disappointment. Some sleep with animals of the same sex as them. Some wish to be cured. Others would prefer society to be cured, after which they and their beloveds would walk in Hyde Park, go skating and dine at Le Caprice.

Bestiality has always existed. I discover that a 25,000-year-old French bone painting depicts a lioness licking what no nice cub would. Cleopatra reputedly kept a box of bees with which she pleasured herself. Egyptians enjoyed crocodiles (you must turn them over first), goats and baboons. The Greeks immortalised bestiality in myth when Zeus appeared to his lovers in the form of a bull, a serpent, a swan, a stallion and a pigeon. The Roman emperor Claudius executed women with rape by stallion. Constantine the Great (who converted Rome to Christianity) was nicknamed "Cow-fucker". The Mosaic commandments did slate bestiality, but then Jews won't even eat lobsters.

What prompts the bestialist or zoophile to reach out for his cow? I turn to the psychiatric texts. Freud believed an attraction to the sexually immature (children and animals) was substitution for a "proper" object - but he never did get on with his wife. Other causes are believed to be sexual deprivation and the absence of human love, the need for an outlet for trauma, the desire for deviance, an expression of anger, isolation, fear of abandonment (a chicken has always got time), a yearning for unconditional love or post-coital silence and a constant proximity to animals.

One psychiatrist questioned by Miletski claims that the desire to have sex with animals is buried within the id. His theory states that man is an animal who developed by evolutionary accident. The beast lies drooling under layers of artificial consciousness. I like this theory but, in the irritating language of psychobabble, we have a large cold buffet of "multiple possible determinants".

What is the legal status of bestiality? It is forbidden in Kansas, but then so is oral sex. There is a global hotchpotch of responses. In England, bestiality is still technically punishable by lifetime imprisonment, so offenders are prosecuted for assault or indecency.

But the zoophiles are gathering. They want acceptance and seek emancipation. They resent the stain of bestiality and a love that dare not squeak its name. We await a furry Oscar Wilde and a barnyard Stonewall cheering him on to the European Court of Human Rights in Strasburg.