It’s not every day that you climb into a £350,000 car dubbed the Veyron killer and get invited to put your foot down on Britain’s fastest test track. Naturally you don’t ask too many questions in case the owner changes his mind or the rain starts again. Or the health and safety people hanging around in high-vis jackets slap a speed restriction on the circuit.

With hindsight, it would have been wiser to have waited for a briefing on some of the car’s more eccentric features. For example, it has no electronic stability program or traction control, which means there’s nothing to stop the wheels spinning on a wet track. Also, it lacks the kind of safety features you’d expect in a supercar. Airbags? No. Wing mirrors? One. Crumple zone? At 250mph, that would be the driver. In fact this is not so much a car as a bomb with some wheels and carpet attached.

Officially known as the GT9, it’s called a Veyron killer because in tests it has reached 300kph (186.41mph) in just 17.6sec, 0.6sec quicker than the Bugatti, and its top speed is claimed to be 254.77mph, a shade faster than the 253.81mph Veyron.

On inspection, its 4 litre engine appears to have been assembled from elements of the periodic table from aluminium through to zirconium, including a 24-carat-gold air intake (to keep the ingoing air cool, the designers specified a metal with particular thermal properties, which happened to be gold). It produces 987bhp – nearly twice the power of the ultra-light Lamborghini Gallardo Superleggera. And thanks to a carbon fibre and Kevlar body it weighs the same.

When you press the throttle and lift your foot off the clutch – which is custom-built to withstand the forces let loose – it feels as though a large sumo wrestler has appeared from nowhere and sat on your chest. The engine is housed in a glass-topped bay inches behind your head and the sound is deafening. You could scream for help and no one would hear you – and by the time you’ve finished driving you probably will. But the striking thing is that the rate of acceleration doesn’t diminish as it does in most fast cars; it increases. Just as the sumo wrestler has stood up, the twin turbos burst into action at 2500 revs and he sits back down again. At this point the scenery outside starts rushing backwards and you can almost see the bow wave of air in front.

Obviously you’d expect wheelspin in first gear in a car such as this. But in second, third, fourth and, er, fifth? I was still being pushed back in my seat as the digital speedometer showed 282kph (175mph) and the long straight at the Millbrook track, in Bedfordshire, ran out, pitching me onto a banked curve.

For a moment the steering went soft and the tyres lost grip. I had a vision of careering into the barrier and splintering into a thousand pieces. Treasure-hunters would have had a field day finding bits of gold and platinum along the trackside. A moment later the car corrected itself and slowed to a comfortable 75mph.

To understand just how crazy the GT9 is you need look no further than the CV of Jan Fatthauer, the man who created it. A professional auto-engineer, he trained with RUF, a German company that tunes Porsches to trouser-igniting performance levels. After a while, he decided that RUF’s Porsches weren’t daft enough so in 2001 he branched out on his own and named his new company 9ff after his wife, Frauke Fatthauer.

So far, 9ff has built three GT9s and has 17 more on order. Most have been bought by the kind of playboy Russian gas barons who you know will crash them into a palm tree in Monaco on their first outing. He plans to build no more than 20. “Any more and it would no longer be an exclusive car,” he says. Really? A car this absurdly quick will always be in a class of its own, it seems to me.

The GT9 is not an official Porsche product and, if asked, the car maker will distance itself. Privately, though, it takes a close interest in 9ff’s engines because of the kind of tolerances they are built to and the stresses they can endure (“You made a titanium con rod that can withstand what?”). The company is located in Dortmund, in Germany’s industrial heartland, which is convenient because its engineers have only to pop next door to one of the hundreds of auto-component factories and ask Herr Müller or Herr Schmidt to knock up, say, a diamond crankshaft.

The GT9 is loosely modelled on a Porsche 911 GT3 but the similarity is superficial – it shares only 2% of the components. It’s lower than the GT3 and longer and the engine is in the middle of the car instead of the rear for better weight distribution.

There’s no doubt that Fatthauer and his team have built one of the world’s fastest cars. I ran out of road, and nerve, long before I got it to its claimed top speed but, judging by its performance, I have no doubt it could achieve it. In a way, though, it’s an academic point.

The Shelby Supercars Ultimate Aero reached 256.18mph on part of a closed-off public highway in Washington last October, beating the Veyron’s 253.81mph top speed in the process, and taking the Guinness record for the world’s fastest production car.

The rivalry among car makers, large and small, has turned into a global arms race. Ever since the Veyron was launched in 2005 it has given every backstreet workshop a target to aim for and suddenly everyone’s making supercars. The question is, by building a car that can beat the Veyron, have you produced a Veyron killer? The answer is, technically yes but practically no.

Guinness defines a production car as “one of a batch built for sale” so the GT9 does technically qualify but when most people think “production” they are really thinking “mass production”. None of the challengers to the Veyron, GT9 included, will be produced on the same scale as the Bugatti, which will run to 300 cars, half of them already sold.

The Veyron is designed as a 250mph-plus road car from its first bolt to its last rivet. The chassis, the tyres, the transmission, the cooling system – all were tested with the kind of rigour you’d expect for a Volkswagen Golf. If you bought a GT9 you’d need to give it the kind of love and attention that only an enthusiast could afford.

That doesn’t mean the GT9 is not as good as the Veyron to drive. In some ways it’s more fun. The Bugatti is so smooth and soundproofed you could pop to the shops and forget you were driving a supercar. The GT9 is a frenzy of noise and excitement. Plus for the price of a Bugatti you could buy two GT9s and have enough change for a Rolls-Royce Phantom.

So all credit to Fatthauer. He’s given me an itch I want to scratch. There’s no track in Britain fast enough for the GT9 to be tested to its limits. In fact 9ff uses the A44 autobahn between Dortmund and Kassel for routine speed trials, at night. It’s perfectly legal, apparently – there are no speed restrictions – though the section of road is long enough only to get the car to 236mph. All the same, it might be wise to avoid that stretch after dark.

To experience the car at full speed, Fatthauer has invited me to the ATP track at Papenburg, northwest Germany, which is used by Mercedes-Benz for developmental testing. The high-speed circuit there is an oval with two 2.5mile straights and curves banked at such a degree that you hardly need turn the wheel. You just drive as if in a straight line. “You can reach 300kph on the banked sections,” Fatthauer says. “Then you just push it a little bit more on the straights and it will happily exceed 400kph.”

Er, right. It’ll be a piece of cake.

Vital statistics

Model Porsche GT9, made by 9ff

Engine type 4 litre flat six twin turbo

Power/torque 987bhp/711 lb ft @ 5970rpm

Transmission Six-speed manual

Fuel/CO2 5.2mpg to 25.9mpg / n/a

Performance 0-60mph: 4.2sec. 0-186mph: 17.6sec

Top speed 255mph

Price £350,000

Road tax band n/a

Verdict Your trousers will catch fire

Rating

Date of release Now

The opposition Model

Porsche 911 GT2, £131,070

For Brute force tempered by clever suspension and traction control. Much cheaper

Against A measly 204mph top speed

Model Bugatti Veyron, £985,000

For A genuine supercar, but manageable enough to take shopping

Against It makes 253mph feel ordinary