Jaguar's not going to launch it for another six months, but Autoblog UK has been given an exclusive first drive of what could be the most important and best-selling version of the 2012 model year XF – the 188bhp 2.2-litre turbodiesel version.

This new version of the XF, is powered by the same 2.2-litre, four-cylinder diesel that's also currently fitted in another of Jaguar Land Rover's models, the Land Rover Freelander and the upcoming Range Rover Evoque.

What's interesting about its fitment in the XF, is the "north-south" installation, which wasn't as easy as it sounds, as new components required include a new oil pan, timing drive cover to allow for a lower bonnet line, heat shield, fuel line and engine mounts.

Other changes for refinement and efficiency include a new water-cooled turbocharger, stainless exhaust manifold and closed loop exhaust gas temperature control.

This engine is mated to a new ZF eight-speed automatic transmission and fitted with a new start-stop system that works on the pressure of the foot pedal - it restarts the engine as soon as your foot comes off the brakes to drive away.

Both the gearbox and start-stop system help this XF achieve a combined consumption figure of 52.3mpg – making it the most economical Jaguar ever and it's green too, emitting just 149g/km of CO2 plus the Euro V emissions rating.

Just because it's the most economical Jaguar ever, don't think it hasn't got the performance you'd expect from the leaper badge, as the top speed is 140mph and this XF completes the dash to 60mph in just 8.0 seconds.

So what was it like on our short drive? Well refined and torquey are probably the best descriptions of this new version of the XF. It's obvious that Jaguar has spent much time with careful sound-deadening as you can hardly hear the four-cylinder diesel rumble at idle or at speed.

The new transmission proves to be a good companion to the engine, making the most of the engines low speed torque and proving to be a relaxing cruiser at speed.

Apart from the new engine, the usual XF model characteristics remain unchanged. These include the impressive body control and of course the sharp steering.

If you're wondering why our XF is wearing exotic camouflage, this model will be a part of a revised range for 2012 which include still secret exterior and interior updates. Prices are expected to start at around £30,000, but be sure that the most economical Jaguar still feels like a real driver's car.