The discovery that BMW’s new M3 CSL would be different arrived some days before the car. I received a letter stating politely but firmly that I was not to let anyone else drive the CSL and that they’d not release the car to me until I’d agreed as much in writing. You might think this a routine procedure among car manufacturers lending cars to the motoring press but it’s not: in 15 years and a thousand tests, this was the first time I’d heard of it. I wasn’t bothered, but it did make me curious.

Then the car arrived, its carbon fibre roof, spoilers and inserts looking as purposeful as its fabulous 19in wheels. Inside, more paperwork. This tranche warned me the car was fitted as standard with very special Michelin tyres that would detach my retinas before losing grip on a warm, dry surface but which consequently required considerable caution on anything else. I also learnt that this particular car had had the 155mph electronic restrictor that is fitted to all other fast BMWs removed and, if a customer wants the same, they’ll have to produce a racing licence.

At first it was hard to see what the fuss was about. This M3 CSL (Coupé, Sport, Lightweight) may be a little more powerful than the standard M3 (360bhp opposed to 343bhp) and 110kg lighter, but its power to weight ratio is still not as great as, say, a Porsche 911 Turbo, while its 0-62mph time of 4.9sec is entirely unremarkable these days; indeed independent tests have shown it to be little quicker than a standard M3. The biggest difference between the two appeared to be the £18,720 more it costs to buy the £58,455 CSL.

But then I drove it and discovered, for want of a better description, a racing car. The modifications required to earn an M3 a CSL badge are legion. Alongside that engine and all the carbon fibre comes revised suspension, modified brakes, quicker steering and a paddle-operated gearbox capable of swapping one cog for another in 0.08sec or, to put it another way, three times faster than you. Inside, racing seats ensure your body can withstand 1.5G of lateral acceleration without depositing you on your passenger, while those who want a tape machine or air-con will need to ask. They’re free but not standard. A CD player is extra.

So forget the mildly disappointing performance statistics and concentrate on the fact, undeniable in these eyes, that the CSL is one of the most hard-core supercars ever sold. Inject some heat into those Michelins and you can negotiate smooth curves at speeds that are, frankly, astonishing. Various buttons allow you to choose the speed of the gearchange, sharpen the throttle response, disable the stability control or programme it for the race track.

And on the track, no doubt, all this works very well. On the road, the CSL is too extreme for its own good as the very things designed to make it go faster than a standard M3 actually contrive to slow it down. In particular, the suspension is so unyielding that, instead of soaking up the everyday lumps and humps, it tends to bounce and skip off them. And the ride is truly terrible. Over one of my favourite roads in Wales I travelled one way in the CSL and the other in a Ford Focus RS — a car with more than 100bhp less and costing little more than a third the price — but what the Ford lost in on-paper power it more than regained by inspiring confidence in its driver. In the end the Ford was just as quick, too. Though I did not try it, I would be amazed if the same could not be said of a standard M3.

So those who have already bagged the 500 CSLs coming to the UK expecting a still faster M3 should prepare themselves: out there in the real world it’s probably scarcely any quicker at all. More significantly, it’s not really like an M3 at all, a car that has bedazzled me with its speed and sophistication since the day I first drove one. An M3 is a road car, an M3 CSL a road-legal track car, and the two should not be confused. The CSL is as harsh, uncivilised and uncompromising as the M3 is smooth, urbane and versatile. There is no doubt at all that, for the money, the M3 is several streets the better car.

All of which leads me to the conclusion that for most people, most of the time, the CSL is a waste of money. Like many things that are bad for you, the CSL is addictive — it possesses a focus that, of its ilk, only Porsche’s more expensive GT3 would recognise. Its non-negotiable demand for your undivided attention can make every departure an occasion, every journey an adventure, every arrival an event. It’s also rare, beautiful and beautifully engineered. To me that is enough to forgive it its many and manifest failings. Just.

VITAL STATISTICS

Model: BMW M3 CSL
Engine type: Six-cylinder, 3246cc
Power/Torque: 360bhp at 7900rpm / 273 lb ft at 4900rpm
Transmission: Six-speed manual
Suspension: (front) MacPherson struts, anti-roll bar (rear) multi-link rear axle, coil springs, anti-roll bar
Fuel/CO2: 23.7mpg (combined) / 287g/km
Acceleration: 0 to 62mph: 4.9sec
Top speed: 155mph
Price: £58,455
Verdict: Like drugs: expensive, dangerous in the wrong hands and utterly addictive