The Jaguar XK120 was so-called because it did 120mph, the XJ220 because it did 220mph. And this is the XKR 75...

So it must do 75mph! Some kind of economy special is it?

We’ll have you know that this is the fastest Jaguar since the XJ220. Instead of the usual 155mph limiter, this one can run on to 174mph before the electronics call time. Without them its top speed would be knocking on the door of 200mph.

What’s the 75 bit all about then? MPG? CO2 output? Forget the eco car thing. It’s called 75 because it celebrates 75 years of Jaguar, and because only 75 will be built.

So what’s special about the Jaguar XKR 75?

It’s the XKR that Jag’s chassis supreme, Mike Cross, would build for himself. So he did. Fist as a hideous green one-off for the 2009 Goodwood Festival of Speed, and now this limited production Road car, which actually made its debut at the 2010 festival. It gets stronger suspension uprights for tighter camber control, stiffer springs (28% front, 32% rear), recalibrated adaptive dampers and slightly wider wheels (up half an inch at the front, 1in at the rear), the back rims wearing 10mm wider rubber too.

The front and rear spoilers are the same as those available on other XKRs equipped with the optional cosmetic Speed Pack, but the deeper side sills are unique to the 75. Every car will come in Stratus Grey, but the silver wheelarch eyebrows are optional.

Any engine changes?

A new exhaust unleashes a mightier roar, hinting at the extra Engine power under the bonnet. When Jag introduced the new 5.0-litre engines last year, the supercharged version actually had to be slightly detuned to preserve the transmission. But the XKR 75 gets an improved torque converter, which means the engine is allowed to deliver the full 523bhp, up from 503bhp in lesser Jags.

Interesting, but I was expecting an XK GT3 RS. This doesn’t sound radically different from the ordinary XKR. Is that how it feels?

Don’t be duped by the modest tweaks – on the road, this XKR is a very different animal. Here is a car that looks like a demure GT but is actually better balanced, more exploitable and just plain more fun than some supercars costing twice as much. Whether you want to get from point to point as quickly, neatly and safely as possible or play hooligan and make the active rear diff earn its crust, this Jag can do it all. The ride is still excellent, the steering loaded with delicate messages and the body control much tighter. Its character isn’t a million miles from that of a regular XKR, it’s just massively better to drive in every way.

And the extra performance is just as noticeable. Jaguar says the 0-60mph sprint takes just 4.4sec, down 0.2sec, but on the road this Jag feels even faster than that. This car was made for those dicey four-car single-carriageway overtaking manoeuvres. Except in the 75, they’re not dicey at all.

The supercharged V8 delivers 483lb ft of torque and spreads it over such a broad rev range that you really have to make a concerted effort to get past the mid-range wallop and explore the top-end performance. There’s a real V8 growl too. Step out of a supercharged XFR saloon and into the 75, and you’d never believe that both were powered by (essentially) the same engine.