Earlier this month, a police force posted a picture online of an aftermarket sat-nav on a car’s dashboard.

It nestled discreetly in the bottom right corner of the windscreen, alongside a police instruction that placing it anywhere else was ‘illegal’.

I forget which police force it was because the tweet has since been deleted. It wasn’t true, you see. The Highway Code and the laws that back it up give no particular location for placing sat-navs, beyond advising that ‘windscreens and windows MUST be kept clean and free from obstructions’, and that ‘glass or other transparent material shall be maintained... [so as to] not obscure the vision of the driver’.

Follow the very letter of the law, then, and you can no more place a sat-nav in the bottom right corner of your windscreen than you can anywhere else.

Although, in reality, obviously you can because if it’s out of the swept area of your wipers, or it obscures only your view of your own bonnet, nobody should really care.

Shouldn’t care, then, but if they think it’s illegal to put it anywhere but the bottom right corner, perhaps they might. Who knows? The daft thing is that if your sat-nav system pops out of the top of the dashboard and gets in the way of the windscreen as standard equipment, that’s just dandy. But your own system, even if it obscures less, may not be. Isn’t this all a bit... fuzzy?

Uber vs London cab vs sat-nav: which is best?

Things are similar when it comes to using a mobile device. Say you’ve installed and programmed a navigation system on your smartphone. I do this because Land Rover’s infotainment system is pants but the Waze app on my phone is excellent. So I strap the phone into a holder attached to a central air vent, which leaves the phone directly next to the car’s own touchscreen. Partly in front of it, in fact.

I could tap away at the Land Rover’s official screen with impunity, so long as I didn’t appear too distracted. Yet ‘it is illegal to use your phone while driving unless you have hands-free access’, according to the Highway Code. And even though it suggests a dashboard holder is an answer, it’s still not totally hands-free, is it? I think the spirit of the law means that, say, if your phone’s ringing, you can touch the screen once to answer it. Motoring organisations think you “should be okay” if, similarly, you’re just acknowledging a one-off navigation instruction. But perhaps you wouldn’t be, depending on an officer’s mood or inclination. And this ‘perhaps’ doesn’t sit that comfortably with me when it comes to legalities.