If you believe the anti-speed campaigners, Britain is full of young tearaways in souped-up Citroën Saxos driving down the pavement at 150mph killing millions of babies. And then being sentenced to three minutes’ community service.

This argument seems to be winning support. There’s a mood abroad in the land that speeding drivers who maim and kill other road users should be sent to prison for 2,000 years. And if the prisons are full they should have huge 6in nails hammered into their heads.

Yes, we’re told, we should treat speeding in the same way that we treat drinking and driving. And doubtless you’re nodding in agreement.

Right. So how come you parked in your flowerbed last night? Because while it’s very easy to say you disapprove of drinking and driving, it’s even harder to get home from a dinner party in the sticks. So like millions of other middle-aged, middle-class motorists you cross your fingers, stick to the back roads and hope for the best.

I’m afraid it’s the same story with speeding. Because while the image of a speeder is a 19-year-old in a turquoise Saxo, we all drive too quickly. Pretty well every single one of us, pretty well every single day.

And how would you like it if you were coming back from a hard day at the office, perhaps not really concentrating, to find that a child has run into the road? You do your best to stop but you were doing 40mph and there’s no chance. So the child dies.

Imagine how that might feel, to know that you have killed a child and that you have utterly destroyed the lives of its family. And then along come the police, who announce that you were driving without due care and attention and that as a result you will go to court.

Will a long prison sentence cause you to drive more slowly in future? What? More than the fact you’ve killed a child? I doubt it. All it will do is quench the natural and understandable parental thirst for revenge. And rob your children for many years of a father.

Anti-speed campaigners argue that a car is every bit as much a lethal weapon as a gun, and that’s probably true. However, while a gun is designed specifically to kill, a car is designed specifically to take your rubbish to the tip and your children to school. If you kill someone with a gun, the chances are you meant to. If you kill someone with a car, the chances are it was an accident. And accidents can only be prevented by something we don’t have at the time. Hindsight.

So what’s to be done? Well instead of campaigning to outlaw excess speed in all its forms, which means campaigning against all of us, we need to target the offensive against those who drive stupidly.

But even this isn’t quite as easy as it sounds. Last week I was following a Renault up the M40 during a streaming wet rush hour. Through the blur of the wipers I could see the tail-lights dissolving into impenetrable spray for mile after interminable mile. Trying to overtake the car in front, then, was completely pointless.

But that didn’t stop our friend in the Renault from trying. He was glued to the van in front of him, veering from side to side and braking every few seconds as the gap narrowed from a foot to three or four inches. Then he’d go by on the inside and begin his assault on the next car in line.

I began to believe he might be a psychopath, or that he had discovered some pressing need to kill himself, so I actually took a note of his registration plate. It began FG55. He knows the rest.

And at this point those of an anti-speed persuasion would urge me to report him to the police. But hang on a minute. He wasn’t speeding. At no point, in traffic like that, did he ever exceed 60. Yes, he was driving like a lunatic, but even here there’s a problem. What if he’s just had a call from his wife to say she was in labour? What if his child had been taken ill? You may say that’s no excuse but I remember well the night my mum phoned to say my dad was very ill. Had I driven up the M1 at the speed limit I would not have seen him before he died. Because I went somewhat faster than 70 I made it in time to give him a hug and say goodbye. Would you have denied me that? We know from official Department for Transport figures that breaking the speed limit is responsible for only 5% of road accidents. It’s rare that I call for balance, but that’s what we need in the debate on road safety.

It’s one big grey area, and that brings me, after a long and rather humourless time — sorry about that — to another grey area where all is not necessarily as it seems. The Volkswagen Phaeton. The dullest way on earth of doing 155mph.

Recently, India Knight tried to argue that men drive fast to impress women. The Phaeton is proof that she’s talking nonsense.

From the outside it appears to be the sort of car your old geography teacher might drive: bland almost to the point of invisibility. You can’t impress anyone with it because it’s nigh on invisible.

But underneath this extraordinarily ordinary body it’s a Bentley Continental GT. Same four-wheel-drive system, same architecture, same incredible attention to detail and, if you go for the electronically limited 155mph 6 litre W12 engine, the same sort of power plant as well. But I didn’t go for the W12, which is one of my 10 favourite cars. I tried the diesel.

So you climb into this exquisitely finished car, adjust the supremely comfortable seat, set the air-conditioning just so, and sit back to admire the eye-scorching simplicity of the controls. And then you turn the key.

You expect the softest of purrs. But what you get is the sound of a Third World building site. What’s more, to make this jolly big car move, you have to give the accelerator pedal a fairly hefty shove. The result is a car that feels as lively as a fire station. This engine is fine in the off-road Toe Rag. But is emphatically not fine in the Phaeton.

Of course at this point dieselheads — who are like petrolheads only with dirty fingernails and nothing interesting to say — will claim that a little extra noise and a slight unwillingness to set off is a reasonable price to pay for all the benefits. To which I say, okay then, what benefits? Please don’t come at me with fuel consumption because this is a 5 litre V10 diesel. Parsimonious it is not, and what’s more it produces more carbon dioxide than a whole flock of cows. And nor is it anything like as fast as you’d hope.

Diesels normally deliver large amounts of mid-range torque and the VW V10 is no different. There’s a whopping 309bhp as well. But somehow this brutality doesn’t make itself felt on the speedo, so you bury your foot into the carpet even more and now the fuel consumption is even worse and there’s a roundabout coming and whoa, heavens above. The brakes are only just up to the job of stopping you.

And there we are, straight into another grey area. Those who buy the big petrol engine will be accused of antisocial speed-driven lunacy whereas those who buy the diesel will be applauded for their environmentalism and their slowness. But which is easier to stop, a rabbit or a brontosaurus? If you are a child, thinking of running into the road, make sure you do so in front of the petrol version, not the diesel.

Almost all cars are ruined by the fitment of a diesel engine. In the same way that all wines, no matter how fine, would be ruined if they were served with a splash of crude oil. But the Phaeton is ruined more comprehensively than any other.

This is a car built to be the last word in discretion. It is a car designed to be as silent and as efficient and as focused as a contract killer. So putting a diesel under the bonnet is like putting James Bond in a pair of wellingtons. The whole point is lost.