Human Condition: Why home for Xmas means a sex-free Yule

'I'll just show Paul his room': Sandra Deeble on the festive segregatio n of consenting adults

You live with your man and your parents have visited you, so they know the set-up. Yet, for that tricky, 48-hour Christmas period, boyfriend is banished to the spare room in your parents' house and those creaky floorboards on the landing put the kibosh on any commuting.

Why do some parents convince themselves that their thirtysomething son or daughter practices celibacy? There are households in which parents fling open the hayloft to visiting offspring and it's business as usual, but for many, the segregated approach reigns. Claire, 31, describes how, this Christmas, her mother assumed the role of B&B owner: "You're in your room as usual," she said, referring to Claire's childhood bedroom, now a shrine, with memorabilia including 100m swimming certificate and pony books. Rob, meanwhile, was shown to the "guest" room, complete with hint of peach decor and a neat pile of Lenor-perfumed towels with matching flannel.

We arrive at our parents' house as adults but, as we step through the front door, a transformation occurs. The separate room routine makes us feel sexless, petulant and blobby. As Claire says, "You might as well put on your Winnie the Pooh pyjamas and have done with it." Some parents even go in for the single-sex dorm approach. One woman and her sister, both in their thirties, tell of when they go home for Christmas with their men. The girls are in one twin-bedded room and the boys in another, the parents' room strategically placed in between to eliminate any late- night antics.

Pippa, 28, said that her parents went to no end of trouble to reconfigure their whole house to avoid any chance of John being within striking distance after dark. As soon as a rock had appeared on Pippa's finger, however, it was time to review the format. "And here's your room," announced her mother, proudly unveiling a spanking new Slumberdown King Size.

Is this just a girl thing? Michael, 33, remembers the occasion when his girlfriend was sleeping in the living room at his parents' house (he was in his old bedroom, racing-car wallpaper still just about visible through the lavish coats of Apple White). "I snuck down during the night to snuggle up with Sarah but fell asleep and when my dad came down early in the morning to let the cat out I was really caught red-handed. My dad was in a silent rage and singled me out while my mum was basting the turkey. He was so unpractised in the vocabulary needed to kick off the conversation that words failed him."

Even in more enlightened families, it seems we would all avoid appearing in the kitchen with flushed cheeks, a sure way to ruin parents' enjoyment of The Archers omnibus. Maybe it is up to us to grasp the nettle. Next Christmas, bring a double futon with you and just whizz up the stairs and roll it out. After all, they're not going to say no and cause a scene. As for me? Well, I had to make alternative arrangements this year as my boyfriend has recently developed a cat allergy. We stayed in the B&B down the road, the one with a massive four-poster bed.