If these prototypes running around jolly old England are what we and spy photographers think they are — it would appear those test mules we saw in September were right — there's a Jaguar XFR on the way as a high-po follow-up to the new XF sedan. There doesn't appear to be a lot of visual differences between the already-revealed XF and this lightly camo-ed XFR, but the quad-pipe exhaust and the huge cross-drilled rotors give away the R-aging 4.2-liter V8 beast within, capable of producing about 500-horsepower. That's right Mr. McGee, you wouldn't like the XF when it's angry. Full spy report from the helpfully quick to the shutter button folks from KGP below the jump.

Our man in the U.K. has snapped the first photos of what appears to be the first full-fledged prototype of Jaguar's upcoming XFR. Although the visual differences are subtle, there are some telltale cues that suggest that this car is something a bit hotter than your normal XF. A new quad-pipe exhaust design hints that this car is running a revised powertrain, and the large, cross-drilled rotors speak of an upgraded braking system to deal with this XF's higher performance potential. Large 20-inch wheels and a noticeably lower ride-height suggests a more aggressive suspension set-up, in keeping with Jag's usual formula for their R-spec cars. Any changes to the front fascia of this XFR prototype are very subtle, and may be limited to this car's blacked-out grille mesh.

Earlier this summer, some mules appeared that hinted that an XFR was in the works. Based on previous-generation S-Type bodies with XF noses grafted on—those mules also had cross-drilled rotors, the same wheels, and a makeshift quad-pipe exhaust configuration. This latest prototype takes those same details, and applies them to a complete XF package, suggesting that the XFR is now in the home stretch.

Our sources from Britain believe that a highly tweaked version of Jaguar's venerable Supercharged 4.2-liter V8, to produce about 500-horsepower, basically matching some of the hottest metal from BMW, Audi and Mercedes AMG. The long-rumored, range-topping XFR-plus (for lack of a better name) may employ a new 5.0-liter engine, and could push power ratings closer to 600-hp. But that car is a good way's off, while this XFR prototype is now running the streets of Coventry, being readied for launch sometime in the next 12-15 months.

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