The mission Transports of delight or the bumpiest ride ever? Olivia Flynn attempts to join the mile-high (and -low) club

his is all about timing. Or that's what I tell Daniel as we click our seatbelts into place and try to ignore the safety demonstration. When I described my latest mission (and more specifically his crucial role in it) - to join the mile-high and the mile-low club - he expressed nothing but willingness.

But now when push has come to a shove, so to speak, my usually up-for-anything boyfriend has got all pale-lipped and jittery. "What if they find out?" he hisses, casting panicked glances at a particularly harridan-faced air hostess. "Relax," I say, not very helpfully, "they won't." Other people's panic makes me exponentially more laidback. Right now he's making me so chilled out about the whole thing I'd be willing to do it here and now while harridan-face demonstrates how to blow into the top-up tube.

We have a whispered consultation. The Italian businessman next to us picks his teeth with a corner of the in-flight magazine. An air hostess who doesn't seem to understand the concept of lipstick being worn only on the lips, looms out from nowhere. "Can I help you with anything?" she trills, her eyes focused disconcertingly somewhere above our heads. "No!" Daniel shouts, at a frightening volume. Italian man flinches and drops his magazine. Air hostess drifts on, apparently unconcerned.

When the seatbelt sign goes off I stand up and head for the back of the plane. As arranged, Daniel - after a short interval - knocks on the door. I slide back the bolt but, due to his extreme paranoia, he shoves at the door before I've had time to step back and I am thwacked painfully in the head.

The act itself is rather strange, possibly because I am suffering partial concussion. The automatic hand-dryer goes off twice; it gets unbelievably hot and oxygenless; and Daniel keeps banging his elbow on the toilet flush so that the air is periodically permeated with the stinging smell of bleach. Afterwards, we discover I've been up against the soap dispenser: we have flooded the basin with nasty almond- flower soap, and I have "press here" printed backwards on my left buttock.

When we board the Eurostar at Waterloo, a week later, we feel like old pros. We've barely found our seats, before Daniel is up and doing a recce. People board the train, sit down, stand up, get off again, wander about the platform, re-board. A completely silent French couple opposite me devour, with the aid of a scimitar- shaped knife, a large salami. Daniel returns: "There are four toilets for each carriage," he announces. The French couple look up, startled, then start mumbling to each other through their mouthfuls of pink offal.

We wait until we're well into the tunnel before we swan off down the aisle. The French couldn't care less. We could wave a packet of condoms in the air and yell, "Guess where we're going?" and they'd just turn back to their Le Mondes. And the toilet is a triumph. Whoever designed it certainly had this purpose in mind. It's three times the size of any other train toilet I've been in, doesn't smell, has lurid pink walls, a nice, ergonomically curved shelf, and - get this - three-way mirrors. It might as well have a sign saying, "Toilet and Canoodling Room" on the outside. So forget mile-high, I'd say. When it comes to transport sex, depth is what matters