BMW 535d

We all know that diesels have come a long way from the rattling tractors of days gone by, but somewhere along the line they have quietly usurped the petrol-powered alternatives. That was the shocking conclusion a few of us faced after testing the sublime BMW 535d on the highways and byways of Southern Spain.

Sixty per cent of BMW’s sales in the UK are now accounted for by the oil burner, a fact dictated by tax regulations based on emissions for company cars, and the US system of economy-based taxation plays to the diesels strengths, too, so it’s a major battleground for the executive brands.

The 535d is as quiet as its petrol-driven sibling and there’s no telltale smoke whatsoever. The only difference is that it’s faster and costs less to run. Diesels are famous for delivering huge thrust in a narrow power band and feeling limper than week-old salad outside of their chosen rev range.

BMW has the answer to this: multi-stage turbo-charging. While, for instance, Jaguar employs its twin-turbos in a side-by-side layout, BMW has opted for an inline set-up. At low engine speeds, the smaller turbocharger does the work and delivers 95 per cent of the available torque at just 1,500rpm. At 2,000rpm, the smaller turbocharger is working flat-out, the larger turbocharger spools up in tandem and all 413lb-ft of torque are available. Towards the red line, a control valve vents some of the gas directly into the exhaust system.

The sequential turbocharger technology means that there is a more or less constant 2.85 bar of boost applied to the intercooler. But the real beauty of this, the most powerful six-pot diesel engine ever in a production car, is that none of this technical mumbo-jumbo will even cross your mind when behind the wheel.

All the investment and innovation is there to convince you you’re not driving a diesel at all.

It took just minutes to plough deep into three figures on foreign roads where the police could only fine us and couldn’t take our precious licence away. Instantly this car felt like a serious sporting proposition, rather than a frugal highway cruiser, and every journalist present took great delight in worrying the 155mph limiter.

This oil burner produces enough torque to rip out trees, 413lb-ft to be precise. That’s almost 30 more than the M5. It’s so much twisting power that BMW can’t offer a standard manual box: it just doesn’t have one that could handle the power.

However, the car doesn’t lose out due to the six-speed auto. It comes equipped with the Steptronic manual operation, but there’s such a reservoir of torque throughout the gears that it’s not exactly necessary and the brakes are so impressive on this machine that I didn’t miss the engine braking afforded by a manual ‘box on the most challenging, twisting and unfinished Spanish road.

It scoots to 60mph in 6.5 seconds and blasts all the way round to its electronically limited 155mph without breaking its stride. The automatic, petrol-powered 530i is 0.6 seconds slower to break the 60mph mark and this is a lifetime in such similar cars.

With this kind of performance, combined with frugality of 35mpg even on a continental thrash and a price tag that starts just the wrong side of £36,500, almost half that of the M5, it’s not just the standard petrol 5-series range that feels threatened by this member of the tractor set.

The sad thing is that, when the diesel is this good, the motorsport badge has become nothing more than a gadget-laden status symbol. Some may throw up their hands in indignation, but if you’re the kind of person that really believes you’ll hit the 8250rpm redline in your M5 on a regular basis, then you’re the kind of person that will spend most of their time on buses at the police’s behest. If it were my money, I’d be keeping a fair chunk of it and putting down an order for this car.

As for the handling, it’s all good news. Not only does this machine hug the road like the proverbial limpet, refusing to wash out into understeer until pushed well beyond the limits of normal road use, it’s also serious fun at low speeds. With the DSC fully deactivated the 5-Series steers on the throttle. Those 272 horses under the bonnet are more than enough to unstick the rear wheels but, when the rear slides out, it’s so easy to hold you could fiddle with the iDrive system with the redundant spare hand.

Fifty-fifty weight balance, achieved with a hybrid body of aluminium and steel in the chassis and thermoplastic body panels, means that despite its 1,660Kg dry weight, the 535d remains a lithe and slinky machine. Active anti-rollbars absorb up to 80 per cent of body sway at lateral forces up to 0.6g, converting hydraulic pressure into torsional strength, which basically means that the harder you lean on this car the harder it tries to stay upright. Although this genuinely does provide sportscar handling without hampering the ride quality, for a truly comfortable ride BMW would have to do away with the run flat tyres.

The interior is uncluttered and functional; the cockpit of a Mercedes might be more luxurious but this one that does it for me. Everything is perfectly situated, easy to use and in the right place, and the styling on the inside has pretty much met with universal approval – unlike the flame-surfaced body.

The styling argument overshadows any piece of technical excellence to emerge from Bavaria these days. But it’s getting boring and the 5-series is still a sexy car, the only problem is that it has replaced a perfectly proportioned luxury machine. The sport kit, M alloys and Imola red paint job on my test car, combined with the soothing effects of two days in Spain, certainly worked for me, though. Pictures don’t really do justice to the car and each time I see one in the flesh that feeling of grudging acceptance has moved further along the axis towards actually liking the design. The back end certainly isn’t its best side, but from the front, and tarted up with the accessories, the 5 is desirable.

On the trip I also drove the impressive 630i -- and we'll be reporting on that car soon -- but for 2,000-mile drive back to England I only wanted the keys to one car. That was the diesel, and that speaks volumes - the days of the tractor are over.