According to its maker, the Alpina D3 is the world’s fastest diesel production car, which is hardly surprising given that it mates the regular BMW 3-series’ four-door bodyshell with 345bhp and, get this, the hardly insignificant matter of 516lb ft of torque.

The D3’s motivational forces are provided by a heavily tweaked version of BMW’s regular 3.0-litre, twin-turbo straight six diesel engine. Internally, the BMW motor is all but untouched but by fitting new, slightly smaller variable-geometry turbos and then tweaking the intercooler and fuel systems accordingly, Alpina has unleashed a fair bit more power and a whole heap more torque.

And the whole lot reaches the road via a similarly tweaked BMW eight-speed automatic transmission, with Alpina’s customary shift buttons being stitched into the back of the steering wheel to enable manual changes. The gearbox software has been rewritten to provide a greater range of characteristics on the move. Select Comfort in the dynamic drive program and both the ride and gearchange responses become even softer and even smoother than they are in a regular 3-series.

Select Sport or Sport Plus, however, and the ride and gearchange responses become sharper and crisper than standard, or so goes the theory. In reality, the spring rates are 40 per cent stiffer all round no matter what program you select, and the anti-roll bars, bushes and bump stops are all bespoke to the D3, too, giving it a more dynamic set of ride and handling characteristics compared with the basic 3-series at all speeds, and in all settings on the move.

Our test car was also fitted with a limited-slip differential (a cost option) and a couple of other choice extras, such as electric leather front seats and a head-up display. Even so, there can be no denying that the basic price of the D3 – just £47,000 – makes it appear exceptionally decent value for money compared with most other saloon cars offering this kind of performance potential.

Pretty much the only thing that’s missing from the D3’s monstrous dynamic repertoire is a genuinely appealing soundtrack. As it is, the 3.0-litre twin-turbo diesel lump produces a nice enough collection of whooshes and fizzes in isolation, and between 4000rpm and the red line it makes a pleasantly industrial kind of sound, but never does it make a noise that could be called satisfying.

Other than that, however, it’s pretty hard to fault, and very easy to fall for as a result. The performance is defined by the seemingly never-ending flow of torque rather than the top end power. As such, you learn to short-shift manually when using the super-fast eight-speed auto gearbox, and that’s when the fairground ride begins in earnest – because what the D3 can do between 2000 and 4000rpm in fourth, fifth and sixth gears is utterly outrageous. And even in eighth at 2000rpm it feels indecently perky.

In short, the D3’s blend of effortless performance with smooth ride and handling is as addictive as it is impressive on the move. You flow across the ground in this car at huge speeds, feeling as if there is almost no energy whatsoever being summoned in the process. In Comfort the ride is deliciously soothing; in Sport Plus it gets firmer and the roll control very obviously becomes better, but even then the ride quality remains better than acceptable, even on the UK’s worst road surfaces.

That’s faintly incredible given that the test car wore 20in wheels with tyres whose sidewalls looked like a band of liquorice. But then such craftsmanship of the suspension settings has long been a speciality of Alpina’s, and the D3 is perhaps one of the best examples so far.

The steering feels similar if not identical to that of the regular 3-series, and there’s no shame whatsoever in that. It’s accurate, precise and clean in its responses, even if the last tenth of feel remains absent from the mix.

The D3’s trump card, though, isn’t its smooth ride and handling, or its tidal wave of mid-range performance, or even its quietly breathtaking good looks. It is instead the fact that it manages to combine all of the above with 50mpg real-world economy – and a price tag that is the right side of £50,000. And that makes it one of the most desirable four door cars that sensible money has ever been able to buy, if not THE most desirable.

If you want one, make sure you get your order in fast because rumour has it that the waiting list for the D3 is already long, and getting longer. And it’s not exactly difficult to work out why.

Top 5 Compact saloons

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