Ireland’s best-kept secret is a stretch of toll road through its capital city that was about to ensnare me again.

The M50 Dublin toll is located between Junction 6, Blanchardstown, and Junction 7, Lucan. And this is aptly named because the bit where they apparently demand payment is so invisible it is worthy of the name Lucan in every sense.

The last time I was caught in this ingenious money trap, I vowed I would never fall for it again

The last time I drove to the UK and back on the ferry, Holyhead-Dublin, I was caught in this ingenious money trap and vowed I would never fall for it again.

On that occasion, I drove at night off the ferry and into the tunnel leaving the harbour, where I dutifully tapped my card on a toll barrier. The next thing I knew, I tapped again at a second toll plaza, and, as I drove south, a few more after that. A month later, when my redirected mail got to me, I discovered I owed more than €50 in fines for not paying another toll I hadn’t seen.

Incredibly, there is a stretch of road between two toll gates with a dimly lit purple overhead sign bearing a relatively small-print website address, and if you could pull up in the middle lane you would see that this says you must pay by 8 p.m. the next day.

What is inevitably going to happen when anyone not from Dublin passes beneath this sign, and happens to notice it, is very clear. Because you’ve just tapped your bank card on a toll gate a few minutes earlier, and because you tap it again a few minutes later, you think you’ve paid. But you haven’t. After a day, an extra €3.50 is added to the original €3.70; after 14 days another €46; and after 56 days another €116.

This time, therefore, I went online before my crossing and tried to register. The website was strange and told me I had to give them a sum of money that seemed entirely random. They said the balance would be held after one journey, for future use.

So I decided to drive it, then pay it online by the deadline. Big mistake.

I drove off the ferry, tapped through the toll gates, drove beneath the sign, and when I got home, logged on to eflow.ie and this is what it said: ‘The eflow website is undergoing maintenance and is currently unavailable. We apologise for any inconvenience caused. Don’t worry, we will be lenient regarding any delay in making a payment during this period. Thank you for your patience.’

Lenient? What a cheek. This period? What period? There was nothing about when the system would be back up and running. I found a telephone number and a recorded voice offered one option: if you think you have received a fraudulent message from us, press one.

I had, in a way, but I didn’t press one. I waited and there was no other option. It told me no one was there.

I had nightmares all night and woke in a cold sweat thinking: ‘I will not give Leo Varadkar another €50!’

I logged in and the same message came up. Website down. It was getting on for 11 a.m. and I had nine hours to find a way to pay €3 before Leo got €50 when I rang the phone line again. This time the options were spelled out only in the Irish language. I guessed that if I said and pressed nothing, maybe I would get lucky, and I did. A lovely girl called Shannon answered.

She put in my registration, asked again, retyped it. Nothing. Whereupon she admitted to me that the cameras don’t always transmit the registration plates by the next day. Or the day after that.

‘I’m sorry, you’re losing me now. So if the system doesn’t come back saying here is your car and here is the amount, before the deadline, how can I pay?’

She told me I would have to leave an amount of money on the system for when it did transmit the image. So she put through a payment of €3.70 and emailed me a receipt, even though the computer insisted that nothing was owing.

‘Just out of interest,’ I said, ‘do you know the average time it takes for the camera to register a vehicle, so it shows up when the driver logs in?’

There was a sigh before she said: ‘It could be two minutes. Or two hours. Or two days. Or a week.’ She said it like that, with disgusted pauses. I could tell she thought this was the biggest con ever.

It ought to make us Brits feel better, because we tend to think we’re hard done by with stealth taxes. So take heart. At least Sadiq lets you log in to be swindled.