When Caterham agreed to lend us R400 BAD it was agreed a number of us should take turns at driving and writing about it. To date you've had the view from the hardcore road-race contingent, flame-haired trackday maestro Roger Green and swarthy Caterham Academician Jethro Bovingdon, both of them Seven fans down to their Nomex underwear and dinky little racing boots. They laugh in the face of danger and tweak the testicles of discomfort.

Well, now you're going to get the view from the Radio 4 shipping forecast Kind Hearts and Coronets slightly soft contingent.

A tip for people like me - 6ft-ish, 40-ish, built for comfort rather than speed these days. Don't attempt your first entry to an R400 if there's an audience. And if the hood's up, don't attempt it at all. I did, and the sense of claustrophobia as I wrestled with the four-point harnesses and side-screens was pretty much what I imagine pot-holing to feel like. I had to force my backside down into the racing bucket - unless you have the hips of an oiled snake, you really need the wide-bodied 7 SV - there's not much elbow room either, and the pedal area is so tight that some drivers are forced to drive shoeless. In the end I struggled out - not the work of a moment - took the hood down and got wet, but at least it didn't feel like climbing into a barrel wearing a straitjacket.

But since then I've had drives where everything - including the harnesses - has just clicked into place. The other night was one of those heaven-sent late-spring evenings when there's enough warmth still in the atmosphere so you don't have to get dressed up like an arctic explorer - or a motorcyclist - to enjoy a 7. It was one of those days you just had to take the long way home. And the R400 was absolutely mind-blowingly stupidly good.

It doesn't sound much cop when it's idling, like a kilo of bolts in a cement mixer. But under load that Xpower K-series fairly tears the air apart. And it fires you forward with such angry potency. You think you're accelerating fiercely, then you discover the throttle's only half way down. Press it all the way and all hell breaks loose. Suddenly you're ripping down the road, the torque whipping up those big rear boots while you lever the gearchanges back and forth, as rapidly as you can, up through the six tightly stacked gears. Waaarp - waaarp - waaaaaaarp. With each new slug of power you feel the rear of the car going light, and when it starts to snake in fourth at 70mph-plus you know what 400bhp per ton really means.

When you come back down to normal road speeds the R400 feels unhappy, the diff chuntering away like it's ingested a bag of spanners, the suspension crashing around. But when you let it loose again it all just works. The suspension, those front wheels bobbing around in full view, is firm but never seems to get seriously unsettled and the trade-off is the most absurdly high steady-state cornering speeds. It is a very physical experience - the whole car pulses to the engine's industrial metal beat. With shortarm jabs at the tiny, chubby-rimmed wheel and the alloy gearknob, barely protruding from the centre tunnel so short is the lever, you batter journeys into submission. It's full-on, just about as big a hit as it's possible to get in a road car.

Apart from those moments when you're absolutely on it, the pleasures are harder to identify. If you drive at six or seven tenths as you might occasionally in, say, a TVR, you can almost sense the car tut-tutting and rolling its eyes. When everything's right it's totally awe-inspiring, but you have to pick your time and your roads. I guess it's good to discover your limits - including what you're prepared to put up with to get your driving thrills. Some people drive their 7s every day, but for me it could only ever be a second car. I guess I am now officially middle-aged.

The Caterham, on the other hand, is in the rudest possible health. The rear arch, which had come adrift in a trackday incident involving a cone and a Rick Pearson, has been replaced (΂£450). And a service (΂£175) has cured a flat-spot that had been interrupting the engine's onslaught. Now, who's next?