The new Alpina D5 Biturbo is ‘the meanest green car on the planet,’ according to the manufacturer.

Which is a fair enough assumption to make, given that the car has 347bhp, a whopping 516lb ft of torque and can hit 62mph in 5.1sec before bludgeoning its way to a top speed of 171mph.

But the numbers that distinguish the Alpina D5 as something a little bit different to the hoards of other high performance German mega-saloons, are these; 155g/km and 47.9mpg.

Not too many years ago such meagre emissions and fine economy statistics would have been the preserve of a decently competitive supermini. Now you can get them with supercar-slaying performance as well. In our book that makes the D5 one of, if not THE most relevant performance saloon cars of the moment.

And while we’re talking numbers, how does a list price of less than £60,000 grab you? Alpina thought long and hard about its pricing strategy for the UK, and in the end decided to go as lean as possible – on the basis that until BMW’s own ultra-high performance diesels go on sale, the D5 will have the market virtually to itself.

So Alpina didn’t want to put potential customers off with a sky high asking price. Quite the opposite, in fact, yet the basic specification of the car remains excellent, with top quality leather, sports seats, xenon headlights and Parking Distance Control all appearing as standard. There's even a Touring version available for those who need more space.

On the road you can tell that the D5 has been touched by Alpina’s magicians pretty much from the moment it starts to move. The car’s standard fit electronic dampers have been retuned to offer a far wider variety of set ups, so Comfort + offers a more soothing ride than in a regular 5-series, while at the other extreme Sport + becomes firmer and more aggressive.

In any of its settings, however, the D5 somehow manages to feel fluid and in tune with the road in a way that the standard car never quite replicates. Partly that’s down to the tyres, which are non-runflat Michelin Pilot Supersports (the same as those fitted to the M5); partly it’s a result of Alpina’s retuning of the springs and dampers.

Either way, it enables the D5 to glide along UK roads in a way that the 535D (which forms the basis for the D5) can’t compete with.And what separates the D5 even more obviously, not just from a 535d but any other car we’ve ever driven with a diesel engine beneath its bonnet, is what happens when you put your foot down and hold it there.

The initial response isn’t quite in the same league as an M5, as the 2993cc straight six takes a great big breath through its two turbos before the moment of the truth arrives. But when it does, wow, the D5 lunges towards the horizon as if it’s being dragged there by a higher force.

The flood of torque, allied to the speed with which the eight-speed Switchtronic gearbox (also retuned by Alpina) picks off gears provides the D5 with a unique style of performance, one that in its way feels every bit as monstrous as what’s on offer in the latest M5. And it does 47.9mpg.

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