Just where does one draw the line between normal, kinky and outrageous? Is it prudish to decline a ménage à trois, amateurish to avoid anal sex and dreary not to play dressing-up? Are you a little too '50s, or have you got a pervert on your pillow?

We examine some sexual fantasies, and asked the experts to assess them.

He wants to have a threesome
Dr Marlene Wasserman (Dr Eve) says: "A threesome is a most difficult situation, as it's potentially a wrecking of one's relationship. No matter how much discussion takes place beforehand, you can never know how you'll feel the morning after. It brings out our jealousies, personal insecurities about our bodies and sexual performance, and makes us question our partner's true feelings for us and vice versa."

He wants to dress up/role-play
Dressing up is a very common sexual game, and extends from sexy lingerie to the dominatrix-in-leather-and-latex scenario. US sexologist Dr Robert W Birch says: "Many people worry about their fantasies being too 'kinky', but such fantasies are really quite common. Unusual fantasies can help maintain arousal and are harmless, provided there's no compulsion to actually experience an act that would be emotionally or physically harmful to oneself or to others."

He wants to watch porn
"This is sure to make you both horny, if you allow it to," says Dr Eve. "Be warned, however, if he needs to do this every time he wants to be sexual with you. It should be in addition to sex, as something different and to learn something new." And Dr Birch endorses steamy flicks as an effective sex-booster: "Novelty can get lost in long-term relationships," he writes. "When a couple becomes comfortable and familiar with each other sexually, they often forget to be romantic." So the odd porn flick is recommended for spicing up a staid sex life.

He wants me to swallow
Dr Eve's advice is practical: "If you don't like swallowing, learn how to lick around the head and shaft of the penis, and learn to recognise when he's about to ejaculate (or have him tell you), so you can remove your mouth while continuing to stimulate him with your hands. Tell him you love him and lust after him, and that not swallowing doesn't diminish any of these feelings. It's just a personal preference."

He's into golden showers and wants me to wee on him
"Watersports may not be your thing but if you feel it's fun and harmless, go for it," advises Dr Eve. "However, if it becomes habitual and he needs it at every sexual encounter, then a conversation is necessary," she cautions.

He wants to try S&M (sadism and masochism)
"S&M is a term used to describe a very broad range of alternative sexual activities," comments Dr Eve. "But it also requires people to be educated about what they're doing, as novices can hurt themselves. The fun part can be going onto the Internet and researching it together, and this may be stimulating enough without having to actually act any of it out." She stresses that safety and consent are essential prerequisites to spanking, caning, bondage and blindfold games and adds that if any doubt exists on this score, it's better not to proceed.

He wants me to use a dildo on him
"No assumptions should be made because a guy enjoys anal penetration, it doesn’t necessarily mean he’s gay." says Dr Eve. "Anal play is a highly stimulating experience for a guy because his prostate is being caressed, and this creates the urge to ejaculate which is very pleasurable for him. Check your own comfort level with this. It's better to cover the dildo with a condom and use plenty of water-based lubricant. "Never insert it into your vagina straight from his or your anus, though, since you could be transferring bacteria which could lead to an infection."

He likes to dress up as a woman
According to Dr Levinson, this is a very common desire. "Cross-dressing or transvestism doesn't indicate homosexuality: in their normal lives, many of these man are totally macho. "However, as with all other fetishes, the trick is to get consent. If your sister comes to see you every Thursday night, but she's really your husband in drag, it can be tricky for any visitors!"

He wants me to shave down there
"Pubic shaving can be a very erotic mutual pleasure," says Dr Eve. "However, if he needs clean-shaven genitals to get turned on, it can be a problem, unless you're comfortable with the girlie look."

He wants to have sex in a public place
"How public?" queries Dr Eve. She points out that there's a huge difference between a surreptitious clutch beneath the tablecloth at a restaurant, and full-on sex in the main street. Dr Levinson says: "When a partner needs to do this, then he or she is no longer interested in loving. Public sex is for people who enjoy getting their thrills from the risk of being caught, rather than from each other. It's a sad substitute for mutually rewarding sex.

So where's the line between acceptable and unacceptable? "It doesn't really exist, other than in the mind," says Dr Levinson.

"The key is to ensure that there's consent, understanding and total comfort in both partners before indulging in any sexual fantasy or fetish. The only real boundary is when a practice or fantasy involves pain, humiliation or coercion in either partner, or when it verges on practices like paedophilia (wanting to sleep with a child) or bestiality (sex with animals). In such cases, professional help should be sought at once."

And Dr Eve sounds another cautionary note: "Some activities, like threesomes and S&M, have become popularised through the media, but that doesn't mean couples who choose not to practise them are abnormal in any way."

"It's all a matter of perspective, and above all keeping sex playful, loving, warm, safe and consensual."

Definite danger areas:

If your partner expresses any interest or fantasy involving any of these, it's time to get help or run fast.

What do you think about fetishes, fantasies and kinky sex? Share your views below.