If you’ve spent any time at all on the internet, you’ve probably at some point come across at least one Russian or Chinese You Tube video filmed with a dashboard-mounted camera.

You might have spent hours giggling at hilarious Russian driving standards (and they really are that bad), or maybe you saw something fatal that you’ve never been able to forget.

Dash-cams are, on the face of it, objective observers in the event of an accident. They can tell you who cut across whom, whether or not a person was tailgating the car in front or even whether they ran a red traffic light.

For simple things like that, the idea is theoretically sound as long as the footage is tamper-proof. Here lies the problem that, as technology and the law stand, makes it impossible for dash-cams to work.

Dash-cams are by their nature removable, and with a USB lead, people can plug them into their computers and use editing software to cut out the bits that don’t suit the story they gave to the police.

For example: “Oh, looks like I ran three red lights at 20mph over the speed limit before the crash. Best cut that bit out before I send the footage…”

This, ultimately, puts the legal notion of the truth, the whole truth and nothing but the truth rather to one side. People are able to supply just the bits of the truth they want the authorities to see.

Cyclists are, in my opinion, the main domestic offenders at present. Endless videos litter video-sharing websites showing helmet-mounted camera footage of taxis cutting riders up, buses pulling out and HGVs turning across them.

But who knows how many pedestrian crossings the rider flew across inappropriately prior to that footage, or after it? Who knows how many pedestrian-only footpaths they rode on? How many red traffic lights did they ignore? How many other Highway Code violations could we tot up on a single trip to work?

Simple, you might say. Make the cameras tamper-proof and force camera users to supply the whole journey’s footage. Then there’s no escaping your own behaviour.

But that’s only one angle; one side to the story. Really you’ll need the on-board footage from the cars or bikes behind and around the person in question, which multiplies the hypothetical workload to impossible levels.

And then think: with all this footage going to the police, how many minor infractions do you yourself commit on a day-to-day basis, even if you weren’t involved in the accident being investigated? It’s all there on film. Do you fly down the wrong lane and then push into the one you really want, to beat the queue, for example?

Do you always stick exactly to your lane on roundabouts? I’m betting not. Who does?

If the police could manage such an epic workload trawling through all the footage they’d receive, we’d soon see another meaning to the video camera’s 25fps. Forget frames per second: it’d be more like fines per second.

At the end of the day, dash-cams can’t work. Instead, all the serial bad drivers can at least be thankful for our chronically under-funded police service. Brilliant.