Jaguar is planning two supercharged versions of the forthcoming XF saloon, in a break from a tradition in which the blown engine is usually reserved for a single, high-performance ‘R’ derivative.

At launch at September’s Frankfurt motor show, the S-type replacement will be announced with a 420bhp 4.2-litre supercharged engine, but it won’t wear an ‘R’ badge and will go without the more extreme wheel/tyre combos, body kit and tuned chassis expected of an R-badged Jag.

The first XF to get the full ‘R’ badge will appear in early 2010, when a supercharged 5.0-litre V8 is launched.

This British-designed engine, Jaguar’s biggest-ever V8, has direct injection and is all new, borrowing only basic design concepts from the venerable AJ-V8, first launched in the 1996 XK8.

The supercharged 4.2 and XF-R will be offered together in the model line-up, a decision likely to be popular in the US and UK. Some diesel-dominated European markets are likely to drop the regular 4.2-litre supercharged model.