FEW would question BMW's time-honoured claim to deliver ‘the ultimate driving machine'.

Things have moved on at a considerable pace in recent times though, to the point that the word eco added to the premium manufacturer's catchphrase.

Everyone has their own name for the greenest models in their stable. There's the BlueMotion of Volkswagen, BlueEfficiency of Mercedes-Benz, EcoDynamics from Kia and GreenLine from Skoda.

In BMW's case EfficientDynamics is the buzzword - and it has made the latest 5 Series saloon a lean, mean taxbuster.

What the Beemer boys have managed is to slash tailpipe emissions from 125 to 119g/km, taking it below the 120g/km mark where significant tax advantages kick in.

That means exemption from road tax in the first year - £30 annually after that -  and a 13 per cent benefit in kind rating for company car drivers.

But it's not just business users who will appreciate this model, as there's also a near 10 per cent boost in fuel economy over the standard 520d to 62.8mpg.

In fact so confident is BMW that drivers will achieve at least the claimed economy figure that it now has an EcoPro gizmo on the trip computer showing additional mileage the car has returned.

So what exactly is EfficientDynamics? Well it's a package of refinements that improve aerodynamics, regenerate brake energy, apply fuel-saving Start/Stop measures and offer gearchange prompts.

Performance, meanwhile, remains virtually unaffected, figures of 0-62mph in 8.2 seconds and a top speed of 144mph possible via the standard six-speed manual gearbox. Automatic transmission isn't an option with EfficientDynamics.

Otherwise every other aspect of the car is classic 5 Series - a premium blend of comfort and function.

With the 2.0-litre four-cylinder diesel engine producing 184bhp, the EfficientDynamics costs a bit more than the standard 520d at £30,435, yet is still low down the series price range.

The interior may appear a bit drab with only a few brushed alloy panels to break up the utilitarian blackness, but you do get leather upholstery and 17-inch alloy wheels.

And true to form it's a terrific car to drive, with the option to switch between Comfort and Sport modes depending on mood.