Focus: Why we love a bad boy

What is it about bad boys? After seven months on the roller-coaster, Kate Moss seems to have no intention of giving up her bad boy extraordinaire, Doherty, the lead singer of Babyshambles. Ditto Sienna Miller. Following weeks of crisis talks prompted by the revelation of Law's infidelity with his children's nanny, Sienna may not yet have put the engagement ring back on her finger but she is reported to be back at the couple's home. Miller is young, rich, beautiful and intelligent enough to know that if he's done it once ... yet it looks as if she's going to forgive him. It's Jerry Hall and Jagger again.

"The point about bad boys is that they're not all bad," says Virginia Ironside, agony aunt of The Independent. "No one falls for a shit. When they're charming, they're very, very charming. Their goodness becomes an addiction."

Roger Pomphrey spent 11 months making a documentary with Doherty, screened on BBC3 tonight. Beforehand, Roger was told: "Everyone falls in love with Pete." He didn't, although he was "enamoured and intrigued" by a young man he describes as "very charming, endearing and open, very, very vulnerable, witty, intelligent and sharp. He values loyalty and honesty and has the genuine courage to lead life in a manner which he chooses. And he's very sexy."

From a safe distance, we can't get enough of bad boys like Pete. They represent the rawness and chaos we desire but fear, and usually with good reason. Doherty and his like may as well have "this way for emotional suicide" tattooed across their foreheads.

But bad boys are fun. "Rule-breakers are exciting," says Phillip Hodson, fellow of the British Association for Counselling and Psychotherapy. "They get your adrenaline running." It is no coincidence that "dangerous" relationships often follow or break out of "safe" ones, when we've had our fill of secure and are ready for a walk on the wild side. Think of Moss's thoroughly decent ex, Jefferson Hack, now consigned to babysitting for their daughter. Or Brad Pitt, who dumped girl-next-door wife Jennifer Aniston for Angelina Jolie, a woman who wore the blood of her previous husband around her neck. (Yes, there are bad girls too. Relate says that its client base is expanding all the time as women adopt the characteristics they have long criticised in men.)

Several years ago, a friend described her sister's "perfect" husband: "He's loyal, earns decent money, helps out with the kids, listens to her, and you know what I'm going to say don't you? He's boring." My friend is now a single mother after discovering that her own "exciting" spouse had been sleeping around for years. In time-honoured fashion she would now be delighted to meet a man like her brother-in-law. Or would she? Despite their protestations, some people seem destined to yo-yo from bad to safe to bad, or to seek out bad every time. "Bad boys appeal to people who are a bit insecure or lacking in confidence - who need a special fix," Ironside says.

What insecure people actually need is a steady Eddy: but what they often can't resist is the frisson of two fractured souls recognising each other. "Alcoholics and addicts in particular are very sensitive people with real warmth and feeling, and they are very sensitive to others' needs," Ironside says. "They can spot unhappiness and talk to it. It is amazing to be on the receiving end of that."

And once he's opened up your soul, a bad boy is unlikely to judge what he finds there. A woman who revisits an eating disorder when she's stressed described to me how her boyfriend, an affable alcoholic, caught her throwing up after a binge and said: "It's all right, I understand, don't I?" "That was so amazing," she said. "I never thought I would be loved like that."

Lots of nice people, especially women, are riddled with guilt about their darker thoughts and urges, but these become piffling beside the sheer range and depth of a bad boy. You can get angry and the roof doesn't fall in. And you get to feel like a beacon of sanity beside him. You become the stable one for a change.

Pomphrey says that, away from the spotlight, Kate and Pete's relationship is "very normal, very loving". Let's hope it works out. There are only so many times we want to watch the Liz Taylor and Richard Burton story again.

'I was just totally addicted to him'

Emily Brown had an on/off relationship with 'X' for a couple of years when she was 36.

"I met X at a party and thought he looked like trouble and kept my distance, but he sidled over to me and threw up on my feet. The next day we were sitting next to each other in church, as prospective godparents. He seemed oblivious to me while I reeled from the alcohol on his breath. I thought I'd better keep a barge pole between us, but after I read a poem during the service his interest in me was renewed. At lunch he kept bellowing across the room in a suggestive way. He was obviously a bad boy.

"He'd ring me periodically but I made excuses, and it wasn't until a year had passed that we eventually ended up going for a drink - one that lasted three days! He made me feel the most beautiful, sexy and loved girl in the world, but I sensed he was bad news. I knew I shouldn't get sucked in, but I did. We'd spend a few heavenly days together and then he'd vanish. I put everything on hold to be with him, and while we were together it was fantastic. Then he would go, and I'd sink.

"When he wasn't with me I knew other girls would be taking my place, because he told me so. I blocked my ears. I was totally addicted to him. He was a notorious man of rock'n'roll who always managed to end up in some lethal situation.

"Although I became the least important of his girlfriends, I couldn't close the door. However hurt I was, when he turned up at my place my anger evaporated."