Road Test: BMW 5 Series M550d 5dr Auto

I'm shuffling at about 60mph on a busy autobahn in the BMW M550d when, with precise Teutonic timing, the traffic spirits away to reveal the glorious black-on-white road sign announcing a derestricted stretch of motorway.
 
As is only polite in such situations, I flatten the accelerator... and experience something so entirely transcendental that it leaves me in no doubt I'm driving the greatest diesel ever made.
 
70mph, 80, 90, 100... the increments tick off with the regularity and ease of an Olympic swimmer's resting heartbeat. 110, 120, 130, and there is absolutely no let-up in the absurd acceleration. 140, 150... and the M550d slams into the 155mph limiter with a force that suggests it's barely warming up. A two-tonne diesel exec saloon has dealt the German limit of decency an almighty slap on the arse and I am already figuring out which family members I can sell to afford one.
 
It isn't simply the rate that the big, bulky 5-Series launches from normal to highly illegal speed that's so brain-scrambling. It's the absolute effortlessness of the endeavour, as if the M550d is a mere Corgi model (the toy car, we mean, not a Crufts entrant) flicked across a kitchen table by a dismissive giant.
 
Perhaps this is not surprising when you look at the numbers. The M550d is the most powerful diesel BMW has ever produced: the triple-turbo (three: it's the new two!) straight-six dishing up 376bhp and a barnstorming 546lb ft of torque, shoving the M550d to 62mph in 4.7 seconds: barely slower than the M5. But even those awesome figures don't tell the full story: the chorus of turbos serves up full twist from just 2000rpm, meaning that monstrous clout of torque is on hand in even the most benign of situations.
 
Though it'll keep pace with the V8 twin-turbo M5 on almost every road, the M550d isn't really an M-car. Not because it'll do 45mph and emit just 155g/km of CO2, but because it's four-wheel drive. This is less of a problem than you might suspect.
 
The M550d is far less nose-led and inert than, say, any modern quattro Audi, feeling entirely rear-drive until you're about to get a heartfelt introduction to a lump of Armco, when it feeds the power to the front wheels with almost undetectable subtlety. I drove it on an icy, snow-strewn German back road and can't think of much - short of a Veyron or Aventador - that would go faster under the stewardship of a ham-footed driver like me.
 
If, like an optimistic fisherman, you've got the feeling there's a massive catch on the way, you're right. But only if you live in the UK. Or Japan. Or Australia. Or Lincolnshire. Or any other country that drives on the left. Because, if you do, you can't have the M550d: at least, not with the wheel where it should be. BMW says the four-wheel drive system gets in the way of flipping the steering wheel from left to right, so it'll only be offering the 550d in left-hand drive markets.
 
The lovely tri-turbo engine will reach countries that drive on the correct side, but only under the bonnet of the X5 and X6. This is scant consolation. We suggested to the BMW engineers that the solution was to make a rear-drive M550d. They disagreed. So Top Gear has decided there is only one solution: we are decamping en masse to Germany.  OK, we don't speak the language, but Google Translate is pretty infalliable, right? Steigen Sie an Bord unserer erotischen Vergnügen Auto!