Don’t laugh, I instruct myself. Be mature. Don’t laugh. I clamp my lips together, but I can’t stop a little giggle escaping.

I glance at Luke, and his lips are clamped together, too.

Then the woman starts chasing her ice cream down the road, pug dog in tow, and that’s it. I can’t stop myself giggling. And when the pug dog reaches the ice cream before the lady, and starts trying to get the lid off with its teeth, I think I’m going to die laughing. I look over at Luke, and I can’t believe it. He’s laughing helplessly, too, wiping the tears from his eyes. I didn’t think Luke Brandon ever laughed.

“Oh God,” I manage at last. “I know you shouldn’t laugh at people. But I mean. .”

“That dog!” Luke starts laughing again. “That bloody dog!”

“That outfit!” I give a little shudder as we start to move off again, past the pink woman. She’s bending over the ice cream, her huge pink bottom thrust up in the air. . “I’m sorry, but pink velour jogging suits should be banned from this planet.”

“I couldn’t agree more,” says Luke, nodding seriously. “Pink velour jogging suits are hereby banned. Along with cravats.”

“And men’s briefs,” I say without thinking — then blush pink. How could I mention men’s briefs in front of Luke Brandon? “And toffee-flavored popcorn,” I quickly add.

“Right,” says Luke. “So we’re banning pink velour jogging suits, cravats, men’s briefs, toffee-flavored popcorn. .”

“And punters with no change,” comes the taxi driver’s voice from the front.

“Fair enough,” says Luke, giving a little shrug. “Punters with no change.”

“And punters who vomit. They’re the worst.”

“OK. .”

“And punters who don’t know where the fuck they’re going.”

Luke and I exchange glances and I begin to giggle again.

“And punters who don’t speak the bloody language. Drive you crazy.”

“Right,” says Luke. “So. . most punters, in fact.”

“Don’t get me wrong,” says the taxi driver. “I’ve got nothing against foreigners. .” He pulls up outside Harrods. “Here we are. Going shopping, are you?”

“That’s right,” says Luke, getting out his wallet.

“So — what’re you after?”

I look at Luke expectantly. He hasn’t told me what we’re here to buy. Clothes? A new aftershave? Will I have to keep smelling his cheek? (I wouldn’t mind that, actually.) Furniture? Something dull like a new desk?

“Luggage,” he says, and hands a tenner to the driver. “Keep the change.”

Luggage! Suitcases and holdalls and stuff like that. As I wander round the department, looking at Louis Vuitton suitcases and calfskin bags, I’m quite thrown. Quite shocked by myself. Luggage. Why on earth have I never considered luggage before?

I should explain — for years now, I’ve kind of operated under an informal shopping cycle. A bit like a farmer’s crop rotation system. Except, instead of wheat-maize-barley-fallow, mine pretty much goes clothes-makeup-shoes-clothes. (I don’t usually bother with fallow.) Shopping is actually very similar to farming a field. You can’t keep buying the same thing — you have to have a bit of variety.

But look what I’ve been missing out on all this time. Look what I’ve been denying myself. I feel quite shaky as I realize the opportunities I’ve just been throwing away over the years. Suitcases, weekend bags, monogrammed hatboxes. . With weak legs I wander into a corner and sit down on a carpeted pedestal next to a red leather vanity case.

How can I have overlooked luggage for so long? How can I have just blithely led my life ignoring an entire retail sector?

“So — what do you think?” says Luke, coming up to me. “Anything worth buying?”

And now, of course, I feel like a fraud. Why couldn’t he have wanted to buy a really good white shirt, or a cashmere scarf? Or even hand cream? I would have been able to advise him authoritatively and even quote prices. But luggage. I’m a beginner at luggage.

“Well,” I say, playing for time. “It depends. They all look great.”

“They do, don’t they?” He follows my gaze around the department. “But which one would you choose? If you had to buy one of these suitcases, which one would it be?”

It’s no good. I can’t bluff.

“To be honest,” I say, “this isn’t really my field.”

“What isn’t?” he says, sounding incredulous. “Shopping?”