##bmw530.jpg --Right##WITH all the speculation, confusion and evident muddled thinking over the Government's controversial 'green' vehicle excise duty proposals, BMW has shot a devastating bolt right through the diesel debate - and it's one that presents fresh evidence for the merits of diesel. Coming shortly after the announcement of the 320d, whose 2.0-litre 136bhp four-cylinder turbodiesel redefines standards in the premium upper medium class, the six-cylinder 24-valve common rail diesel-powered 530d seemingly delivers the impossible: high performance, class-busting economy and industry-leading exhaust emissions, questioning - even ridiculing - the wisdom of reducing road tax on smaller, supposedly greener, cars further. In all but badging, the 530d looks identical to its petrol-engined stablemates.

With a power output of 184bhp at 4,000rpm and peak torque of 288lb-ft at just 1,750rpm, the 530d claims its place as the most powerful production diesel car in the world. The bald figures are enough for a top speed of 141mph and 0-62mph time of 8.0secs, while the payoff for such an impressive torque figure is blistering through the gears pace: 50-75mph in fourth gear takes just 7.2secs - and that's faster than the V8 petrol-engined BMW 535i. And yet combined cycle economy of 39.2mpg is comparable with many conventional family saloons. It's a clear 10mpg better than the petrol 523i's combined consumption figure of 29.1mpg, while the 528i manages 28.5mpg. The old 525tds, by comparison, achieved 34.9mpg.

That's a deeply impressive set of statistics, but it's not until you climb behind the wheel of the BMW that the engine's brilliance really shines. At tickover, it is barely discernible as a diesel, while the absence of smoke emission on start-up or during acceleration dispels any embarrassing pollution worries. In fact, with two catalytic converters equipped with preheat to minimise the time taken to reach optimum operating temperature, and full exhaust gas recirculation, this engine is one of the cleanest diesels in production. There's even an auxiliary heater system to warm the engine coolant and cabin in cold weather: it's claimed the extra heater reduces the time taken for the engine to warm, cutting emissions further.

On the road, turbo lag is much reduced, particularly compared with its predecessor, the 525tds, and with 70% of peak torque arriving at just 1,300rpm the performance piles on deceptively rapidly. In normal motoring you can almost consider dispensing with the gearbox altogether such is the engine's train-like pull: third gear provides tremendous flexibility while overtaking is easily accomplished in fourth. There's seldom any need to exceed 3,500rpm, even though the engine's peak revs are at 4,500rpm, and with such a flat torque curve the reassuring seat of the pants acceleration is particularly evident during overtaking.

What's more, it's accompanied by crisp throttle response that's light years removed from the lethargic delivery of comparable indirect injection rivals, not least the 525tds. There isn't much engine inertia between gearshifts either, which smooths gearchanging.

On its own, the 530d's performance is worthy of deep praise but when refinement levels are taken into account, the BMW becomes little short of astonishing. Wind and road noise are as subdued as in any 5, and engine roar is muted to the point of being virtually inaudible at normal road speeds. Under acceleration, the straight-six produces a distinctive thrum that actually sounds quite sporting.

The 5-series' dynamic ability needs no introduction here. If there's a slight nose-heavy tendency owing to the diesel engine's added weight, it's compensated by the suspension's compliance: this is still a wonderfully well-balanced car. Even the pot-holed, tight-cornered roads of our test route failed to upset the 530d's impeccable poise and handling balance, leaving just a supremely rewarding drive. In fact with such little call for gearchanging, this is truly the ultimate lazy driver's car.

For those wanting a touch more body control, BMW is planning a new Sport series of range additions aimed at the more sporting driver, though it's unclear which engines will be available the enhanced suspension package. As with all 5s, traction control is standard on the 530d meaning there's no chance of any unwanted wheelspin - a consideration given the engine's prodigious torque. BMW's excellent five-speed automatic transmission with Steptronic manual control is available at £1,220, arguably the ideal partner for the diesel engine.

With the new common rail engine's clean-burning characteristics, BMW has extended service intervals, the frequency being indicated by the dash-mounted service interval indicator. On average, an oil change is required at 13,600 miles, though careful driving may see this stretched to 18,600 miles - a 30% improvement over the old 525tds which needed attention between 7,500 and 15,000 miles.

CAP Future Residual Values awards the 530d SE a three-year/60,000-mile RV of no less than 50% of cost new, a figure no doubt influenced by limited supply: next year BMW will sell about 1,200 530d saloons and Tourings in the UK. Available in both saloon and Touring forms in SE trim only, the 530d goes on sale now priced at £29,235 (525tds SE £27,810) for the manual saloon, £30,455 for the automatic. The Touring adds £2,050 to those prices, at £31,285 for the manual (525tds SE Touring £29,860) and £32,505 for the automatic.

Without doubt, the 530d is the finest diesel car we have driven. Its combination of driver appeal, refinement, performance and economy blows the anti-diesel debate wide open and should sway the opinions of even the most hardened diesel-haters.