It's just not possible to hold a dignified conversation when a pair of strangers are conducting a live bed show right in front of your nose, says Anna Maxted
There's a bit at the end of An Officer and A Gentleman where the hero sweeps his lady into his arms and strides through the crowds snogging her. Everyone else cheers and claps and wolf-whistles. Likewise, there's a bit in Every Slushy American Film where the hero sweeps his lady into his arms and strides through the crowds snogging her. Everyone else cheers and claps and wolf-whistles ... Perhaps in the USA it's traditional to greet those who get frisky in public with a standing ovation. In the UK it's more likely that they'd be doused with a bucket of cold water.

British people do not approve of public displays of affection and justly so. Couples who saunter dreamily along Oxford Street blissfully entwined, pausing for a little kissy and oblivious to the fact that a million shoppers are desperately trying to overtake them because Marks & Spencer shuts in 20 minutes, are a nuisance and should be confined to canood-ling in sparsely populated areas such as Canary Wharf. And as for lovers who neck with gay abandon in City bars - they should be arrested for trespass. Don't they know that the likes of Corney & Barrow are strictly reserved for hard-working bankers, journalists and accountants who wish to extract huge pay rises from their bosses by alcoholic means?

People who get passionate in public cramp our style. How can you continue a dignified conversation with a business partner when a pair of strangers are conducting a live bed show right in front of your nose? You can't, because the collective attention is inevitably hijacked by the proximate hanky-panky. Your colleague appears to be listening but his eyes are flickering nervously towards the animated exhibition of foreplay. You and he are not intimate enough to acknowledge the fact that people are making love in front of you, so you absorb your embarrassment, and - as when you took your inquisitive goddaughter to the zoo and the rhinos decided to mate - ignore it.

Of course, there are exceptions. Public displays of affection are grudgingly permitted at weddings, for example. After being pronounced man and wife, the bride and groom are allowed a three-second smooch while all the guests look on and say aah. But even then, the caress is a carefully choreographed token in the chaste traditions of a 1950s screen kiss. There are certainly no tongues involved. The bride doesn't want to smear her lipstick, and the bride's mother doesn't want her daughter to shock the priest or rabbi. Nor does she want her young nephew to cause a family rift by attempting an X-rated imitation smacker on little cousin Letitia.

While most of us suspend our disapproval on such occasions, we resent other people's displays of mutual lust intruding upon our daily grind. For instance, the misery of travelling on public transport is sacred and should not be profaned: "I find it depressing to see other people snogging furiously on the platform," says Amanda Jakes, 28, from south London. "But that's because I split up with my fianc two months ago, when I found out he was cheating on me, and I'm not in the mood to witness people joyously disappearing down each others' throats. I think it's bad manners actually. You wouldn't leap on your boyfriend in front of your parents. So why do it in front of strangers?"

Possibly for that very same reason. If you are infatuated with your partner you don't give a fig for the rest of the world: if you fancy a quick game of tonsil tennis while you're waiting at the bus stop, what do you care if some old granny tuts disapprovingly and the bloke in the pinstripe suit doesn't know where to look? You don't know them, you don't notice them. However, if your mother was also queueing for the No 46, you'd probably attempt to restrain yourself because, well, she's your mother, and getting stuck in to a passionate clinch with your lover would be disrespectful to her as she'd feel like a big green gooseberry. Anyway, she'd probably thwack you on the head with her umbrella.

Indeed, the most devoted practioners of public displays of affection suddenly turn coy when faced with a relative. They can't even face being third party to it. Most people would rather sit through 12 bumper editions of Pets Win Prizes than watch two minutes of Nine-and-a-Half Weeks if their parents were in the room. As for the sight of teenage brats Michael and Danni slobbering over each other in Neighbours - most of us can barely stomach being present ourselves, let alone sharing the experience with an older family member.

My pal Joanne - occasionally spotted necking in Waitrose - is 24 and quite grown up, yet she recalls with mortification when, last Christmas, she and her boyfriend Andy settled down to watch a film that contained a fair whack of steamy love scenes, and her father decided to join them. The poor girl spent half the time in the kitchen shouting frantically "Do you want some coffee?" while Andy remained grimly on the sofa next to her father, praying that the television world would spontaneously combust.

Such double standards develop at puberty; possibly at the excruciating moment when one of your parents corners you on the subject of the birds and the bees; you weren't happy chatting about the process of reproduction with your mother and father then because it was too gross, and anyhow, Lucy McDonald from class 2B had explained all there was to know in lurid detail. Twenty years on, that juvenile reluctance doesn't seem to have dwindled. Anyway, your parents forfeited their right to the particulars of your love life when you shyly announced, aged 14, that you were going out with Michael across the road, and your father roared with laughter and said: "Woooo!".

As far as Joanne is concerned, parents - sheltered from their offspring's romantic antics - are the lucky ones. She says: "If I see other couples frantically groping each other in the supermarket I think `Ugh, save it for the bedroom.' I think it's distasteful, it's like saying `We're in supreme one-ness and the rest of you can lump it'." She then adds: "But if I want to fling my arms around my boyfriend and kiss him to death by the frozen chickens, then I will, and I don't care what anyone else thinks."

A tad unfair, surely? "Yes, but Andy and I are in supreme one-ness."