Your vital male organ. How come it’s only with your vital organ that size doesn’t matter? I mean, no one’s girlfriend ever said, “Of course size doesn’t matter, I don’t care what size the diamond is, or the handbag, the bra, the divorce settlement.” Whatever they say, size always matters.

But with cars, oddly the ones that get women waggling their little fingers at drivers are not the huge strap-on substitute beasts. No one ever looks at a bus driver and says he must be deficient in the trouser department. It’s speed and cost that draw attention to the Y-fronts.

I’ve no idea how the size of car got confused with good in bed. Personally, I’ve always thought that it’s men on stilts who are probably trying to compensate for nature’s deficiencies. Size and its place in a fluid and judgmental society has been occupying a lot of my thoughts recently.

You see I progress in a Bentley, and by any standard of measurement a Bentley is a big car. Measured in poles, rods, perches, chains and bushels, there is a lot of Bentley.

Now I know you’re going to ask me what sort of Bentley. Well, it’s a dark blue one with seats the colour of an autopsy buttock. Before the blue one, I had a yellow one with seats the colour of a Senegalese heavyweight. They said the yellow was chrome; actually it was renal failure specimen yellow.

And before that I had a Rolls-Royce, with ancient leather that was like the heel of an old Chinaman’s foot and a body the colour of a skinned cow’s tongue. That’s not my description, that’s what Rolls-Royce calls it – lange de boeuf. I like these big cars; I like their size.

Most cars are like hotel rooms; they all look the same. The guy who gives you the key says, “Can I show you where everything is?” and you say, “It’s okay, I know, I’ve stayed in a hotel before”. You don’t have to open the glove compartment to know there’s a Gideon Bible-sized manual that you’ll never look at, just like the one in the hotel.

But a Bentley is like a suite: the guy with the keys says, “Welcome to the Gondolier Suite” or the Presidential, or the Imperial. “Let me show you around.” The favourite simile for driving a Bentley is that it’s like some bit of furniture. It’s like driving a sideboard or a cocktail cabinet or a Chippendale hostess trolley. Actually, it’s like driving a honeymoon suite, though the sanitary truth is that like hotel suites you never use the extra room. There’s a boot you could pack the entire cast of The Sopranos in, and under the bonnet there appears to be a medium-sized nuclear reactor.

I love the Bentley. I love it because I’m a very bad driver and if you’re a very bad driver you like to have a good 6ft between you and the thing you’ve just hit. The Bentley has the displacement of the Graf Spey and the construction of the Flying Scotsman. The engine is like a stampede but the bit you sit in, the bit you spend your time in, is remarkably poky. Some might say with all the puffed-up leather and the hand-turned knobs and the callused woodwork it’s actually quite cramped. Even in the honeymoon suite the bed is just a bed.

I say I progress in the Bentley but the truth is I progress less and less. It sits outside my house like a Yorkshire alderman’s caravan and I wheel my bike round it. So I’ve decided, with regret and rue, to sell it. I’m going to get a Mini. Little and Large; Cannon and Ball; Morecambe and Wise. The Bentley’s the funny one, the Mini is the stooge. I could have just kept the bike, but then that’s like only having a tent.

The Mini Cooper S is a tardis car. It pretends to be small and neat and sylphlike, but the driver’s bit inside is huge. It’s about the same size as the Bentley, but it’s an Ian Schrager boutique hotel room rather than a Connaught.

It’s all design gimmicks that aren’t an improvement. Is that a tap or does it turn on the lights? The most annoying feature is the speedometer, the size of a soup plate, as if bigger makes quick faster. There’s another digital speedo behind the wheel – fast, faster and faster still. This is a little motor that wants you to think it’s Kate Moss. A pretty, naughty, goer.

When you stand it next to the original Issigonis Mini you realise how corpulent we’ve become in 40 years. What it’s actually like is a contemporary comprehensive kid compared with a skinny free-milk kid of the Sixties. The BMW Mini is a little chubby oik: it isn’t Kate Moss, it’s Jamie Oliver. Still all knock-me-back chat, ducking and driving, it has put on a couple of chins, indulged in a bit of chub.

The best thing about the Bentley, apart from the air-conditioning system that was the equivalent of six chest freezers, and came on chillier than a Ukrainian model’s knickers, was the fact that it is completely déclassé. The first thing people say about last century’s Bentleys is, “These are really cheap aren’t they?” They’re the cars that make you brothers in motoring with fourth division footballers, Midlands skip magnates, hippie Somerset baronets and East End video artists. Secondhand Bentleys are “so big that they can park in two style zones simultaneously”. They’re deeply cool and fundamentally uncool at the same time.

The Mini, on the other hand, is the sequel, the remake. It’s the remake of The Italian Job. It’s Life on Mars as opposed to The Sweeney, and it’s German, so cool doesn’t come into it. And it has one massive social disability, worse than being a Somali fundamentalist asylum seeker with drug-resistant TB: it’s used by estate agents. Not just used by them to get from 3bth to ftd ktchn but as a billboard for their ghastly business. The dumbest thing BMW ever did – well apart from the unpleasantness in the Thirties and Forties – was not banning estate agents from buying Minis. And if they did, not unfitting their brakes. Getting over the real-estate smear is a big ask for a fat-boy car but they’ve done it by being properly popular.

One in every five cars in London seems to be a Mini and I rather like the idea of being like everyone else. The great crowd of Minis have clubbed together to drown estate agents in the antichic of a nippy avalanche of runarounds. They are, essentially, big shopping trolleys.

How do the Bentley and the Mini compare to drive? Well they don’t, obviously. Mostly because you never get to compare. Driving in a city is exactly the same whatever you’re sitting in.

It isn’t the velocity or engineering that count. In fact all the dynamism, happy torque and Posturepedic velocity amounts to very little because you never get to experience them. Three or four times in the life of a car do you ever get to feel the carpet with your right foot. What matters is whether you can sit in it for long periods. Is it amiable and comfortable?

And the answer to both the Bentley and the Mini is yes. The old clubbable mock-Georgian library chairs of the Bentley are fine, and the Mini has the ergonomic grab-your-kidneys Milan bar stool business, which is also fine.

The most noticeable real-time business is parking, but then I never fail to be able to park the Bentley. It isn’t as if there are a lot of weeping, bladder-exploding Bentley and Rolls drivers out there unable to stop who only come to rest beached on soft verges when the gas runs out. It’s one of the mysteries of urban life, how everyone gets to park. It’s like musical chairs played with quantum physics.

The biggest difference, and finally the decider between keeping the Bentley and getting the Mini, was that you can’t just nip down to the shops in a Bentley. It doesn’t do nipping. Not because it can’t, but because it’s not in its nature. It wasn’t brought up to nip. Every journey is a sortie. You have to spend a couple of hours in a deckchair outside a wooden hut reading a three-week-old copy of the Racing Post and then someone rings a bell and you have to run out to your crate, do an instrument check, offer a cheery wave to the dog, and fire up the mighty V12, humming the Dambusters march. The Mini you just get in and drive without thinking. It’s only a Mini, it’s just the shops.

Ecologically, there’s no contest of course. The Bentley is far and away the best ecological option. The most wasteful dimension of motoring is car production. The Bentley is near-on 30 years old. It was built in Britain by hand. It had three or four owners before me. It’ll probably have five or six more and go on for another 20 years. That’s impeccable recycling.

It’s also very expensive to run, a three-point turn costs the equivalent of a house in Rwanda, but then environmentalists are always telling us that motoring should be made more expensive.

The Mini, the chubby chaser, also likes a bit of a binge, but in the end the Bentley has a big boot. However, it’s the owner who has to carry the baggage of association. The Mini is an egalitarian; it just says, “I’m probably not an estate agent, but I might be”. And I’d rather wheel my bike round a small penis substitute than a big one.

Vital statistics

Model Mini Cooper S

Engine 1598cc, four cylinders

Power 175bhp @ 5500rpm

Torque 177 lb ft @ 5000rpm

Transmission Six-speed manual

Fuel/ CO2 40.9mpg / 164g/km

Acceleration 0-62mph: 7.1sec

Top speed 140mph Price £16,025

Verdict It might be small but it’s what you can do with it that counts