BMW 730d

Price: £54,160
Top speed: 153 mph 0-60mph 7.2 seconds
Consumption: 39.2 mpg
CO2 emissions: 192g/km
Best for: social climbing
Also worth considering? Mercedes-Benz S-Class, Jaguar XJ, Lexus LS, Audi A8

Is this the best car in the world? It isn't a question you would normally ask about a BMW, not even the limo-sized 7-series, and yet it is pertinent for the British car industry. The reason is that this, the new 7, is the basis for the "baby Roller" project that has been gestating inside the BMW combine for some time, the company having bought the rights to the flying lady and all that some years ago.

Obviously, there will be some important changes; the pocket Rolls-Royce to be sold alongside the gigantic Phantom will be even more refined than the 7, even better kitted out and will, one hopes, retain that all-important Roll-Royce ambience and elegance, symbolised in the fabulously slim steering wheel in the Phantom. However, under all that will be a 7-series, and that is an excellent starting point.

The most impressive feature of the 7 is its diesel engine. BMW is one of a dedicated band of manufacturers who made it their mission to make Rudolph Diesel's old oil burner fit for humans, sporty even. They achieved that at least a decade ago, but this is something else. The straight-six 3-litre unit as fitted to the 730d is, to answer my earlier enquiry, one of the best (if not the best) diesel units in the world. You know the usual adjectives that are applied to decent engines – smooth, powerful, effortless, torquey. Well, it's all true about this one. Subjectively, it compares well with the 5-litre 12-cylinder petrol unit found in the Bentley Continental GT which we tested in these pages recently, though the BMW is only half as powerful. So it would be good enough for a Bentley. Indeed, it is perfectly apparent that BMW have engineered a diesel engine fit for a Rolls-Royce. I suggest that they go for it, reap the whirlwind of publicity for such an audacious act and, ever so casually, also mention that this superb unit will return 38 mpg on a run and has correspondingly low CO2 emissions. A Rolls-Royce to answer the twin challenges of the credit crisis and global warming: quite a tour de force.

The second most impressive feature of the 7, by the way, is the "sideview camera", something I'd not come across before, even on a Lexus, who are usually first with the toys. Not sure what it is for – but it provides a "dog's eye view" of the world from the front of your car. Something to relieve boredom at the traffic lights, I suppose.

And what needs fixing before they turn the 7 into a Rolls-Royce? Well, the handling is a little fruity if you chuck it about, so that needs taming, and the bootlid is excessively heavy to close. An electric motor should sort that in the Rolls-Royce, but they also need to tweak it for 7-series drivers. Otherwise, leave well alone. If you can't wait for the new small Rolls-Royce, be assured that the surprisingly economical and soberly styled 7-series is – nearly – the best car in the world.