Anal sex is not the kind of thing you talk about on a first date. A man can't exactly slip it into conversation over dinner among questions like, "How long have you lived in Notting Hill?" and, "Do you faint at the smell of fish?" But men think about it a lot. Anal sex has a gravitational pull on them because it is forbidden, naughty, messy and literally unspeakable: one mention of anal sex at a dinner party and there will be no more wine for you.

It's not unnatural, though, no matter what your vicar says. If God didn't want us to have anal sex, why can we? If some body parts weren't supposed to go into other body parts, they shouldn't fit at all. The Bible clearly states that the city of sodomites is a lousy tourist trap, but it doesn't say anything about the abhorrent metropolis of nose pickers. If we can put our fingers up our noses without fear of eternal damnation, then anal sex has to be okay, doesn't it? Well, that's my rule and I'm sticking to it.

The really big reason men love anal sex is simply because it's there. Like climbing Mount Everest, the challenge exists. You don't need Sherpas or oxygen, but the thought of doing it casts a large shadow over kids' stuff like vibrators and amusing clown-faced condoms. Anal sex proves to men that they're past the point of being grateful for a grope and they can get all the 'regular normal' sex they want. Asking for and getting anal penetration means you've made it. You're in the Big League.

Say 'anal sex' to a woman, however, and she'll break the world record for the 100-metre dash. Very few women like it really and even fewer will let their lovers even put the tip in. There's even a porn star in Los Angeles - a woman who has done everything and everyone - refuses to open her back door for love, money or stardom.

Women have good reason to dread the trip up the olde dirt highway. Unless they've experimented with it themselves first, men haven't a clue about the incredible pain of having anal intercourse for the first time. If a man doesn't prime his woman properly, there ain't enough KY Jelly in the world for her to forgive or forget. The woman will be pulling on her clothes so quickly the poor chap will only see a blur of natural fabrics and a velvet hair scrunchy flee his flat. The next day when he phones to see how she (and her bottom) is, he'll be greeted with a hissing, "YOU BASTARD!" followed by a slamming click. He'll be confused. She'll be off to casualty. In short, the wedding is off.

Still, men find all sorts of ruses to get their girlfriends to roll over. Inside every missionary zealot is a back door man who longs to hump freely where the sun don't shine. The most successful approaches happen in the middle of a sweaty sex session. She's a wanton animal and the man, pretending to be equally caught up, takes advantage of her lust and whispers (in the same voice he uses when he says, "Let me buy you flowers"): "Let me put it up your bum." Given that he's put it everywhere else, she won't clock the b-word and before she knows it, she's shish kebab. Persuading your reluctant girlfriend to have anal sex is the sexual equivalent of going to an Oriental restaurant and ordering the live monkey brains: it's revolting but it does show that you know what you like - and you don't care who has to suffer for it.

Sex guides are forever offering suggestions for enjoyable anal sex ("massage the area until it is relaxed", "don't stampede for the sphincter", "stop when your partner passes out from the pain"), but you can't follow their advice word for word. They'll send you on a scavenger hunt for the several gallons of lubricant, enema bag, rubber hose, rubber sheets, anaesthetic, doctor on call, splints, tongue depressors and a gum shield for when she turns around and slugs the anal perpetrator in the gob: if you're back there, that's you, bud.

Nobody follows these instructions of course. Anal or otherwise, sex isn't supposed to be something you have to go to boot camp for. It's supposed to be as spontaneous as human combustion. Besides, after a long day at work, nobody looks forward to a pre-rumpy pumpy bowel rinse-out (sex guides tell you that crap just to put off amateurs). Informing someone that anal sex is painful, messy, dangerous and glorious is like the warning on cups of McDonald's coffee telling you that the liquid inside is bloody hot - that's exactly why we want it.

A few women, like my friend Dani, really enjoy anal sex. But even she had to stop because, as she put it, "It feels too good." The eerie feeling of swinging between pain and pleasure, discomfort and bliss, can be addictive.

You will never be able to sit on a barstool again but for some people that's a small sacrifice.

Anal sex is also a lot about power, humiliation and trust. This is why so many people will only fantasise about doing it. Let's face it - they can get all those things from their nine-to-five and not have to worry about permanently stretching certain muscles at the back of beyond. As Freud once said, sometimes a cigar is just a cigar - anal sex can be mere sex in a more interesting part of town as it were.

That doesn't stop us from wanting it, oh no. Its reputation as a forbidden sexual act gives it a huge 'Phooowoar!' factor. For that reason alone, there will always be plenty of new arseholes around.