With over 400bhp under your right foot the XKR is a thrilling and terrifying proposition. Trackside’s Keith Collantine gets thrown in at the deep end.

I’m strapped into a 420bhp Jaguar XKR that’s accelerating crazily with no sign of stopping. I’ve only myself to blame, because it’s my foot on the accelerator.

Next to me the instructor is shouting “full power, full power, full power” like Jeremy Clarkson stuck in a loop.

A sharp corner is coming up fast – I resolve not to brake until he tells me to. But as we fly past the ‘100 metre’ board, he still hasn’t piped up…

Thrash a race-tuned Jaguar XKR around Bedford Autodrome? No problem, I thought. Pump in a few quick laps, crank out a few doughnuts for the cameras, job done.

Not so fast.

Palmer Sports are letting us have a play in their race car fleet ahead of the racing season because they’ve just brought a new technical partner on board in the shape of Comma lubricants.

Brand new for 2007 at the Bedford track are ten 420 bhp Jaguar XJRs.

If that wasn’t a tasty enough proposition, these are tuned for circuit racing.

The suspension is reworked, a roll cage installed and front and rear aero kits bolted on. The most significant change is the gearbox – which they’ve replaced with an F1-style paddle shifter capable of swapping cogs in a thousandth of a second.

The main event is the supercharged 4.2 litre V8 engine. It puts out 420 bhp and pushes the car to 185 mph.

The XKR is so powerful they extended one of the straights by 60 per cent so the car can hit top speed. When someone’s gone to that kind of trouble, it would be rude not to oblige.

I get strapped into the XKR and meet one of Palmer Sports’ very own ‘Stigs’, who shows me how to get the most out of the car.

At first I just tickle the throttle and the beast rumbles forward. Easing it carefully out onto the track it feels exactly like a sleek luxury car should.

My instructor’s first remark of the day is short and direct: “Full power.” I’m going to hear a lot of that.

I floor the accelerator and the engine leaps into life. It doesn’t scream, it growls louder and louder. The power surges like a tidal wave - a relentless, unstoppable wall of torque.

The rev counter leaps to 6,000 in an instant - with a flick of the paddle in goes another gear and still the engine hammers on.

There’s scarcely time to take account of the horizon before it flashes past my ears. The last time I travelled this quickly I was several thousand feet in the air eating peanuts.

The speedometer is ticking past 150mph as I face my corner dilemma. I’m about to brace myself for impact when more instructions are fired at me from the passenger’s seat:

“Brake. Turn. Power.”

Opposing parts of my brain are fighting for control of the car. One side wants to brake as late, turn as little and accelerate as hard as the lunatic next to me is demanding.

The other just wants to stop the madness. Happily, it surrenders.

Chucking the car into corners takes some getting used to. To begin with I ham-fistedly throw the car at the bends, rather than turning in gently and letting its prodigious grip take care of business.

But this kind of detached self-criticism of my driving comes after the event – behind the wheel I’m struggling just to keep up with the car’s awesome capabilities.

It’s unnerving, unbelievably exhilarating, and incomprehensibly quick.

The vast rear wing generates massive grip as the car hurtles along, and the electronic wizardry behind the brake pedal can make even the most flat-footed cretin feel like a superstar. However harshly I jab at the brakes the car remains beautifully composed.

Lairy, Top Gear-style drifts are out of the question. This has been set up to handle like a racing car should with astonishing grip on turn-in and magnificent balance.

Given the car’s weight the back end can come unstuck if pushed hard enough – but it changes direction remarkably quickly for such a big beast.

A dozen laps pass me by in a frenetic blur of action, and suddenly it’s time to hand the car back. Heat soak blazes from its tortured engine and scorched brakes.

Frustratingly, the XKR has raised my expectations of performance off the scale. Where am I supposed to get a speed fix to rival this anytime soon?

The world seems a lot slower now. Damn, I forgot the doughnuts.

Racing round-up

British Touring Car Championship, Brands Hatch

Jason Plato got his championship campaign off to a fine start with two wins. But defending champion Matt Neal triumphed in the third race giving his new Honda Civic Type-R its first victory.

Matt Jackson also shone, taking a podium at his first BTCC appearance in race three, in his ex-Andy Priaulx BMW 3 Series.

Indy Racing League, St Petersburg

Brazilian Helio Castroneves won the second round of the IRL championship after controversially bumping Dan Wheldon out of the lead at one point.

Wheldon’s team mate Scott Dixon finished second and leads the championship. Briton Darren Manning gave his AJ Foyt team their best showing in years, qualifying fifth and running in the top three before spinning.

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