Infiniti's four-door M saloon has, up to this point, arrived on UK shores exclusively powered by a detuned version of the 3.7-litre petrol V6 nicked from the Nissan 370Z, neatly walling itself off from a European market utterly dominated by diesel sales. Now though, Nissan's luxury arm has dropped the 235bhp, 405lb ft, 3.0-litre diesel V6 into the M, in an effort to give it appeal outside of Russian and Middle-Eastern markets, Infiniti having heard only slightly late that parsimony is the new black.
The bare figures are middle-of-the-road rather than astonishing, as you might expect from an engine borrowed from the Renault/Nissan alliance (you can find this motor in both the Laguna and the Pathfinder) rather than something produced for the pseudo-luxe Infiniti brand. The 1,845kg M is persuaded to 62mph in 6.9 seconds, hits 155mph and emits a reasonable 199g/km while managing a combined mpg figure of 37.7.
The engine itself is gruff lower in the rev range, but torquey enough to get the car motivated, happily chuntering through the seven speeds of the auto 'box and making a decent fist of it. Nothing aggressive, though the ride tends toward the thumpy on the smaller GT-spec 18s, and a bit confused on the larger, optional 20-inch rims. The handling is similarly non-specific: there's a rear-steer system that makes the M more lively in corners, but as soon as you approach the speeds that might make it fun, the electronics panic so hard that you just can't be bothered.
The interior has more of the same air of confusion. The Japanese may have invested much time to get the wood to approach the glossiness of mercury, but such over-processing merely makes it look... fake. The Forest AirTM system is just an air-freshener in the air-conditioning, and the Dynamic Safety Shield includes some stuff that surely you shouldn't need if you happen to be conscious. Things like blind-spot intervention, Distance Control Assist, and Lane Departure Prevention - all part of a ‘bubble of protection' that Infiniti sees as a boon to modern driving. It just smacks of ‘things we can market to justify the price'. Which is steep: the M30d may be well-specced, but it still costs nearly £45k basic.
And that's exactly where the Infiniti M30d's problems really lie. The Merc E350CDi, the BMW 530d, the Jaguar XF3.0D S. All cars that you could easily argue a case for. The M? For someone who's being deliberately wilful, rather than rational. So far down the pecking order, you'd have to be crazy.
We like: That the M will get Merc-developed engines in 2012. Individual choice
We don't like: Why would you? Really?
TopGear verdict: There are much better cars out there for less money
Performance: 0-62mph in 6.9secs, max 155mph, 37.7mpg
Tech: 2993cc, V6, RWD, 235bhp, 405lb ft, 1845kg, 199g/km CO2
Tick this on the options list: It has pretty much everything
And avoid this: Metallic paint, £665