Magnificent Seven: The Caterham sports car

You can see the appeal of the Caterham sports car almost without ever meeting one. It's those bug-eyed looks, like a mudskipper plonked on four wheels. In the metal, it's even more charming. The looks are archaic, as the basic shape has been around for half a century, since the days of the Lotus Seven – as the car was known was before the Caterham firm bought the rights from Lotus in 1973.

Every Caterham makes a magnificent sound. The new R400 Superlight model I tried out for a few days last week was more throaty than most: the Ford-derived two-litre unit growled very satisfyingly, though it was most often to be heard screaming through the close-ratio six-speed gearbox.

Things are set up for breathtaking acceleration in the Caterham; it is, after all, a favourite for track days, and this model has taken Lotus founder Colin Chapman's old adage about the way to make a car go faster being to "add lightness" to heart: its power to weight ratio punches through the 400bhp/tonne mark. (With some 210bhp that normally has to lug around a Focus instead of this featherweight.) You hit the magic 60mph mark in less than 3.8 seconds, well into supercar performance territory.

Now, what I ought to have done with this Caterham was to have taken it to a track and thrashed it to within an inch of its crazy, boggle-eyed life. I didn't, though. I drove it from London to Scotland instead. Partly to visit people, but also to see whether, in extremis, the Caterham actually functions as a grown-up practical car. Naturally, it flopped.

Some of its drawbacks were predictable, and unfair to carp on about. The petrol tank is small, so on a long journey you'll find yourself filling up often. I also found that you have to be quite careful with your " trigger finger" on the forecourt. Then there's the cabin. This model uses the slimmer of the two types used by Caterham, and it is a tight squeeze. When you sit in the car it's like being in a bathtub or maybe one of those hot-water spas they have in Iceland.

Nowadays posh cars have something called multi-climate control, where each quarter of the interior can be air conditioned to an individual's tastes. Caterham has a similar, but involuntary, system. Inside, as the driver, your left leg is being baked by the engine next to it whilst your right leg is a frozen drumstick, flat against a thin layer of aluminium as it is. The effect is more extreme when the heater is on, as it pushes arid air against your knees and nowhere else.

From the waist, and particularly your neck up, things are much cooler and fresher generally, and after a prolonged run your ears will feel distinctly disconnected from the rest of you. The Caterham is pretty unaerodynamic, though with so much power it'll easily push through 100mph and much more. It's too noisy for a conversation at motorway speeds and it feels very vulnerable. You're so low, knee-height shall we say, that you can almost hear other drivers saying, "Sorry, didn't see you down there," as they swerve at the last minute to avoid crushing you. Your passenger can expect a very wet bottom if you drive through a puddle; even with the hood up and the "doors" (bits of plastic) popped into place, it is not watertight.

None of that matters. The Caterham isn't supposed to do the job of a Mercedes S-Class or even a Renault Clio in keeping you comfy on boring motorway runs, even if this one will set you back £25,000. It is supposed to function as a second, "fun car": but even so, a Caterham is little trying. First there's that plastic roof. I've tried three Caterhams now and I've never been able to get its pram-like hood on properly. Then the delightful tiny steering wheel is detachable, so your roadster can't be nicked and you can get in and out a little more easily, except that when I tried to put my steering wheel back on it wouldn't go. There's nothing quite so immobile as a car without a steering wheel.

Third, there's the rally three-point harness which is a pain to adjust and get on. So you'll need about half an hour to prepare before starting your journey, an Edwardian sort of delay. Yet in my Scottish travels, I came across a gentleman named Justin Kennedy who had owned the Lotus TNG 7G, once owned by Colin Chapman, and which was given to Caterham as the definitive template for the car.

According to Kennedy the R400 Superlight has all the magic of those originals. He's right, but I'm wondering whether I'm a little too impatient to enjoy the Caterham magic show to the full.