Before a car goes on sale to the general public, its manufacturer performs many tests. Examples are driven in slow motion into walls and other obstacles to make sure they are safe. Doors are opened and closed thousands of times to ensure they won't fall off. And engines are tested in the vast heat of Arizona as well as the frozen wasteland of an Arctic winter.
Then, when a robot has turned the radio on and off four billion times, and sensitive acoustic devices have established it's still making exactly the right sort of click, the finished product is shipped to the Nürburgring where men in cheap trousers pound round and round and round, ordering stiffer sidewalls and harder suspension until the ride is totally ruined. But the car can tear a driver's face off before it starts to slide.
The result of this exhaustive testing is remarkable. Because, by and large, cars are totally bulletproof. Drop your mobile onto a pillow, and the screen will smash. Leave your laptop unattended for a day, and its systems will jam. Ask your coffee machine to make you a cup of coffee, and it will demand a full service before it will even think about obliging. And then it'll decide not to anyway.
But your car? You can drive it down a track so rutted that your teeth all fall out one by one. You can drive it through rain that's so heavy it's no longer see-through. And you can leave it parked in the midday sun. And still, all of its things will work. Most remarkably of all, cars can even survive the toughest environment in the known universe - a week on a TG film shoot.
I'm not talking now about the cars we're filming. They're mollycoddled and looked after. I'm talking about the cars used by the people doing the filming.
Let me give you an example. Top Gear's big cheese arrived on a shoot one morning this month in a brand-new Mercedes E63 estate. A car that had been meticulously prepared for his appraisal by Mercedes-Benz. It gleamed. It shone. And it bristled. Because it had no idea that it was in for the worst week of its life.
Within an hour of its arrival, it had to be moved, and, unfortunately from its point of view, this job was given to a girl. And as we know, no girl will consider driving a car, even 40 yards across a car park, without first making sure she has enough bottles of water for the journey. These are half-drunk then left in the footwells for the rest of time.
When the shoot was over, the Mercedes was driven to the overnight hotel by someone who was plainly going for a new world record - how many sticks of chewing gum can I eat in half an hour. Judging by the wrappers that were cluttering up the centre console the following morning, he managed somewhere in the region of 4,500.
The next day, someone suggested The Stig should be given the job of driving the Mercedes to the second location in Wales. Needless to say, he arrived exactly three minutes before he'd set off. And you could feel the heat from the brakes and tyres over in Nova Scotia.
Of course, because we were in Wales, it rained. And this turned the whole site into something that could easily have been used as a location for a film called Planet Mud. All of which was transferred from the Earth into the car by a selection of cameramen, sound recordists, producers, researchers and assistants.
We know that many of them must have been girls because, half-buried in the thick, cloying soil, were another 2,750 half-drunk bottles of water.
We know, too, that many of them will have been BBC employees because of the way this car was being driven. It is a little-known fact that on the day you are issued with your BBC identification card, you completely lose the ability to drive a car. You lurch from pillar to post, quite literally. And then you mount the kerb.
In the filming world, all people carriers are called Previas. At home, you know full well you're talking about a Galaxy or a Sharan, but when you are at work, it's a Toyota. Similarly, a Range Rover is a vehicle. Unless it has a camera in the back when it becomes a camera car. In the filming world, there is filming. AND NOTHING ELSE.
By the end of day one, the Mercedes was starting to look rather forlorn. Maybe because it sensed that James May had just said: "I'm going to drive back to the hotel in the Mercedes."
James is a very good driver. He really is. A bit slow perhaps, but smooth and safe and a pleasure to be with. But he does break wind a lot. So, by the time we arrived back at the aforementioned hotel, I was pretty much dead. Also, a lot of the soil in the footwells appeared to be boiling. But the car? Actually, I have no idea how it was faring. It had become impossible to see.
The next morning, a female assistant brought it round to the front of the hotel, via a bush and a golf course, which meant another 200 bottles of water were rolling about under the seats. And there was something sticky on the door linings. Also, a bottle of glue used for attaching fake moustaches to people's faces had leaked onto the handbrake. And worse was to come.
There's a rule known to everyone in TV. Never let a film crew into your house. This is because they'll break it. It applies equally to a car. Offer to run a cameraman a hundred yards up the road, and, when you get there, you'll have no rear-view mirror, no interior trim and a shattered instrument binnacle. After two days, the Range Rovers they use to make TG look like they've been torn apart by a monster.
For the whole of the third day, a crew used the Mercedes as a Previa. And not since Nagasaki has the world seen such devastation. I used the poor car that night to drive back to the hotel and have never felt so ashamed. How could we have turned a gleaming press demonstrator into this in just three days? And why, all of a sudden, was there a sausage roll in the ashtray?
It went on like this for days until it wasn't a car so much as a favela. A steaming, pungent, teeming mass of rotting food, bacteria, disease and soil. Which was producing its own new forms of life. If you treated any other machine like this, it would break. If you treated a person like this, they would die. And yet here's the strangest thing.
When the shoot was over, before the big cheese reclaimed his car for the drive back to London, it was taken to a car wash. And in just five minutes, it was returned to a state of showroom freshness. The carpets. The seats. The boot. The paintwork. All looked new. You could not achieve similar results with your furnishings, fixtures and fittings at home, that's for damn sure.
I'm not singling out the Mercedes for special praise here, because over the years I've seen countless other vehicles and Previas recover from a few days in the hands of a BBC film unit.
Apart from Peugeots, obviously.