It’s said that there is a kink for every conceivable erotic proposition, but I can’t imagine that anyone would go out of their way to have an intimate encounter on a narrow mattress with wheels attached.

From bitter experience, I know it doesn’t matter how quiet and careful you are. The bed will glide, slide and bang against the wall, and anyone within a 50-metre radius will come running, assuming that the house is falling down.

My family is warm, welcoming and kind, but also strictly Catholic. Growing up, my castor bed was an effective deterrent against most sexual activity, but when I left home and moved to London, I had a double bed of my own, and they couldn’t stop me from sharing it.

However, when I returned home for Christmas, I was back in the bed on wheels, and any partners who came back with me were sent to a separate single bed. Sometimes on a different floor.

When I started seeing the man who became my husband, he gamely opted to come back to Dorset with me and experience a Buchanan family Christmas. That year, my parents bought a luxurious king-size bed for my room – and stuck my just-married sister and her husband in it. We were given separate, draughty quarters.

On Christmas morning, my husband came downstairs, looking a little shell-shocked, and explained that he hadn’t slept terribly well because it had rained so heavily in the night, and some of the rain had got through the roof and on to him. I was outraged on his behalf. “Well,” replied Mum. “When you’re married, you can have your old room back.”

The reality of sex in a single bed at Christmas