I meant to get the bus, but by the time I arrived at the stop at 5 p.m. last Tuesday, I was running late. I was relieved to see a Tic Tac of orange light floating towards me through the evening. The taxi stopped, I climbed in and said: ‘Just north of Angel please.’ Then: ‘I’m afraid I only have £25 so we’ll probably have to stop at a cashpoint.’ The driver had a flat cap, and in the paler oblong of the rearview mirror, I could see he was wearing sunglasses. I didn’t think to think this strange even though it was dark.

‘Oh don’t worry. I’ll take you for £25,’ said the driver. ‘One of my girlfriends lives up there.’ This was, on the face of it, a kind gesture, but as the doors locked I felt a sudden strong desire to get out.

There’s an anecdote Daniel Kahneman uses in his book Thinking, Fast and Slow to illustrate the power of gut instinct. The story is about a fireman who, on a hunch, pulls his team from a burning building just seconds before it collapses. It’s as if the fireman is clairvoyant, but in fact, below the radar of rational thought, his unconscious mind has absorbed anomalies and demanded action. I think women have, in their bones, the same fine-tuned instinct for predatory men.

The roads were clear that Tuesday. London was still on holiday. As we raced through the dark, I fumbled in my pockets and failed to find the £25. What a relief! ‘I’m so sorry — I can’t find my cash,’ I said. ‘We’ll have to stop after all.’ The driver said: ‘Oh, I’ll do it for nothing. It’s the New Year, isn’t it?’ It was not New Year. It was the third. We hadn’t chatted, let alone become pals, so why the free ride? And why were we heading south?

As we rounded Sloane Square, the driver began to talk astrology. ‘What star sign are you? I bet I can tell. I bet you’re Aquarius.’ I feigned total ignorance of all star signs. ‘I’m really a landscape gardener,’ he said. ‘That’s why I have these here.’ He gestured to a clump of white flowers taped to his dash. Even through the interior gloom I could tell they were fake.

As we raced down I turned the situation over in my mind. It was either very bad indeed or totally fine. Either he was abducting me or I was paranoid. How could I tell? Adrenaline interferes with reason. All I could think to do was try to call my husband, over and over again: Ring-ring, voicemail. Ring-ring, voicemail. I have no idea how I expected him to help.

The driver said: ‘You’re very calm, aren’t you?’ I think, in retrospect, this was irritating to him, because a few minutes later he said: ‘Look, don’t be frightened by my sunglasses. I wear them because I live in the middle of nowhere, in Essex where there are no street lights. It’s totally pitch black where I live and the headlights are bright.’ This made no sense at all. Why wear shades in central London because you need them in Essex? Why wear them in Essex if it’s too dark anyway? ‘Yes, these new halogen headlights are a travesty,’ I said brightly. ‘There should be a law against them.’ He laughed for a long time, right round Buckingham Gate.

I am not the person I thought I was. I spent my childhood quite sure I’d make an excellent detective. In minicabs, I’d memorise the bits of the driver I could see, just in case I could save the day during some later investigation. I often memorised the licence numbers in cabs. None of that occurred to me on Tuesday. I just kept gabbling in a jolly way, trying to make nice.

It’s odd how strong the instinct is to appease someone you think of as a threat. I’m sure many psychopaths depend on it. I wouldn’t have dreamt of calling the police from the back of the cab, for fear of offending the driver. I didn’t even try the electric window, though I wanted to very much, because it was freezing outside and I couldn’t think of a plausible excuse.

The other reason for not reaching for the window switch was more shameful. If it had been locked, it would have confirmed my fears and that was too scary to contemplate. There’s a story Debbie Harry — Blondie — tells about accepting a lift from a stranger in NYC in the early 1970s. It was late at night, perhaps she was pissed, so when a car slowed down, she hopped in. She instantly regretted it. The hairs on the back of her neck stood on end, she said. Inside, the car just didn’t look right. The door handles had been removed, making it impossible for a passenger to get out. Blondie didn’t make small talk or gabble about the weather. Blondie wasn’t a cowering ostrich. She acted on her instinct like that fireman. She slid her arm through a gap in the window, undid the door from outside, rolled out onto the sidewalk and ran away. After his conviction, when she saw him on TV, she realised the driver had been the serial killer Ted Bundy.

As we made for Westminster Bridge, I gathered some gumption. ‘Stop here. I need to get money. I need it anyway for my baby-sitter,’ I said firmly, and he did. He wheeled the cab around and, half–disbelieving, I opened the door and got out. Had I imagined the danger? I paid the driver, muttering something about needing to do some shopping. As I turned away, he said, ‘Wait!’ Then he grabbed a handful of taxi receipt slips from beside him. ‘Take these,’ he said. ‘Make sure you read the back of them. Read it!’ In big red letters on the reverse of each receipt was printed: beware sexual assault.

The next day I got my bike fixed, and I’ve been peering in cab windows as I pedal, looking for men in flat caps and sunglasses, hoping to atone for my cowardice by getting a licence number. I’m not sure what I could report the driver for — who complains about the offer of a free taxi? I am sure, though, that he was trying to scare me, and who knows what a man who likes to scare women will do next?