There is relatively little in automotive technology that is truly new. In the late 19th century, as the motor car struggled for credibility, Dr Frederick Lanchester developed a device called a harmonic balancer – or balancer shaft – to reduce vibration and allow an engine to run more smoothly.

It was to be something for which many a petrol and diesel engine manufacturer has long been thankful. But now Subaru has come up with a “world first” passenger car “boxer” diesel that is inherently well balanced, minimising the nuisance of secondary harmonic vibration – with no need of clever Dr L’s long-used device.

Boxer means that its cylinders are horizontally opposed instead of being in line (or sometimes in a V), which is the norm. Subaru’s petrol engines are also boxers – as are those that power the Porsche 911 – but, after almost nine years’ development, Subaru has fitted a diesel boxer to the latest all-wheel-drive Legacy Sports Tourer and Outback models.

On sale initially (from £19,995) in its Legacy Sports Tourer and Outback crossover all-wheel-drive estate, the new 2.0litre, four-cylinder boxer turbo-diesel will eventually be introduced across the Subaru range.

As well as modest levels of vibration, the engine is quiet when warm, revs smoothly and delivers its turbocharged 148bhp in a delightfully linear flow.

Maximum torque of 350Nm is available from 1,800rpm but there is no sudden surge of urge as there is with many turbo-diesels; the boxer just serves it up almost like a normally aspirated petrol engine. It sounds mildly sporty when driven hard but purrs on the motorway, although there is typical diesel clatter at tick-over when the engine is cold.

Allied to a five-speed gearbox (it needs six), the boxer gives the Sports Tourer a 49.6mpg overall figure with CO2 emissions of 151 g/km, top speed of 126mph and 0-60mph in 8.5sec and the Outback 48.7mpg with 153 g/km, 124mph and 0-60 in 8.8sec.

Dr L may have been impressed by the truly new application of the boxer layout that has no use for his famous harmonic balancer but, being an inventor, would doubtless have said: “Yes, but to make it even better, what about trying . . .”