When I was ­little, my mother used to say: "Never tell a lie, because one lie can turn into a dozen." Mind you she also used to say "I don't know where the chocolate is" when everyone knew she'd stashed it under the fridge, so I never took this advice particularly seriously.

Until one night a while back, when I was in a taxi and realised I'd forgotten an essential item, so asked the driver to stop off. "Anywhere's fine," I assured him. "Petrol station, supermarket, ­pharmacy ..."

"What is it you need?" he asked.

And then I hesitated. Because the thing I needed was condoms.

Now, I think condoms are an ­invaluable and potentially life­-saving invention. What the Pope lacks in ­appreciation for condoms, I make up for. But I didn't want to admit this to the driver. It felt overfamiliar, unnecessary and somehow wrong, as though I were saying: "I am intending to have sex tonight, and you are facilitating this, whether you like it or not."

So I thought quickly and replied: "Cigarettes" (which are not an invaluable or potentially life-saving invention). The driver didn't need to know that I'd never smoked in my life.

He then frowned and repeated: ­"Cigarettes? From a pharmacy?"

Embarrassed, I thought hard again. "Nicorette," I corrected. "You know, those nicotine patches." I was pleased with this, as it suggested he might have misheard.

We stopped off at a late-night supermarket. I bought the condoms (despite a slightly awkward interlude where the cashier asked "Which type?", and I hissed "Any!"), buried them at the bottom of my bag, and climbed back into the taxi, which sped off. All was right with the world.

"Do they work?" the taxi driver asked. For a moment, I thought he meant the condoms. Then I realised. "Yeah," I lied again. "They seem to."

"Are they expensive?" he inquired.

"Not really," I guessed.

"How much do they cost then?"

Oh no. "About a tenner," I told him. It sounded about right.

At this point, I should perhaps have made a concerted effort to swerve the conversation in a less humiliating direction. I should have feigned sleep, changed the subject, or staged a journey-length mobile phone conversation in which I was the only participant.

But I thought that, realistically, the driver would tire of asking tobacco-related questions soon.

Unfortunately, it transpired that he'd been thinking of using Nicorette for a long time, and so he kept up his steady line of inquiry: how long had I smoked for in the first place? Four years, according to my brain. What had been my chosen cigarette brand? Marlboro Lights, apparently. How long had I been on the patches? He kept probing, and I kept lying through my nicotine-unstained teeth, until he asked the question, "So what do these patches have in them then, except for nicotine?"

"I don't know," I answered truthfully. It was, I thought, perfectly acceptable for the sum total of my Nicorette-based knowledge to end there. If the taxi driver wanted to know more, he could find out for himself.

And then he said: "You could always look on the packet."

Feeling panicky, I flushed bright red and pretended not to have heard him. The driver insisted: "You could look on the packet. It'd have the ingredients on."

If I'd had the gall, I could have opened the bag, pulled out the condoms and exclaimed: "You'll never believe this – I asked for Nicorette and they've only gone and given me condoms instead!" But I didn't. I hung my head and mumbled lamely: "I've put it away now."

"What?!" said the disbelieving driver.

"I've put the packet away now," I repeated. It was one of the most excruciating moments of my life. The driver shook his head, and we drove the rest of the way in silence.

That night, I thought back to my mother's advice, and realised I'd learnt a valuable lesson: never leave your condoms at home. Or, if you do, always make sure you're carrying a packet of Nicorette.