Weekend opinion: There's no such thing as free road tax

I remember reading a blog post from an excited Citroen buyer a few months ago – "I've just bought a C1," it read. "1.0, 60mpg, free road tax for ever!"

"Mmm, no," I recall thinking, "free road tax until the government decides otherwise."

A few short months later, it looks like the tide is turning – as, of course, it would. Transport for London is currently discussing the idea of 'adjusting' the current rules on congestion charge exemption, for example, simply because too many vehicles are being waved through for free.

When you look at how many cars currently on sale are entitled to this free day pass into the centre of our capital city, it's easy to see why.

I counted 67 different models that had at least one sub-100g/km engine as an option – and that's a lot of lost revenue for Boris et al.

This is why – among other reasons – I'm baffled by the idea of buying a car simply because it's free to tax. You only need to look at the current system to understand how ridiculous it all is.

What makes the 100g/km mark so special, exactly? Where does that magic number come from? Why isn't it 113 grams? Why not 78.2? There's no rhyme or reason ecologically speaking – it's all just pretty, rounded numbers set by the EU.

Worse than that, they're numbers that force car makers to do silly things. Engines, unfortunately, don't instinctively output metric figures in units of 10, so what tends to happen is that they'll be tweaked to fit in – chasing a largely irrelevant number often at the expense of driveability.

It's all a bit daft, if you ask me – after all, you don't see vineyards watering down their Merlot every time alcohol unit pricing is discussed, do you?

Toyota recently did it with the Aygo – introducing some adjusted, longer gearing that makes the car just that little bit less enjoyable to drive. And what for? To have their work made futile by a man in Whitehall, who suddenly decides he'd like to lower the threshold because it's not making money.

By all means, buy a car because it's cheap to run – that's something where the cost will always remain relative. But for free road tax? You've got to be kidding.

Do you agree? Let us know your thoughts in the comments section below