IT'S the near perfect defence for owners of huge SUVs accused of driving gas-guzzlers.

And the name of the ‘get-out-of-jail' vehicle is a BMW X5 50e, a massively powerful petrol plug-in hybrid that, in our hands, easily squeezed more than 40 miles from a gallon of E10.

That's more frugal than many a 1.6-litre family car from a few years ago!

The X5 model has been around for a quarter of a century in various incarnations, but the latest - and most expensive version - combines cosseting luxury, awesome acceleration and surprising economy. The bad news is that it will set you back around £80,000.

Its considerable urge comes from a 3.0-litre straight six, a 194bhp electric motor and a 25.7kWh battery. Combined, it tots up to a mighty 483bhp, sufficient to transport it to the benchmark 62mph in under five seconds.

Thunderous the performance might be, but the over-riding impression from the tall BMW is luxury. In addition to the obvious frills such as soft leather upholstery, heated steering wheel and electric seats, you get warmers on the door armrests, ambient interior lighting and one of the best touchscreens on the market.

The plug-in powertrain actually offers the best of every world, though even more powerful units are available. It benefits from the sort of instant propulsion only available with the aid of electricity, yet it remains a gentle, easy to drive car for pootling around country lanes are city shopping.

Noise levels are appropriately hushed, unless ‘Sport' mode is selected when things become a tad more vocal as well as sharper reactions. The ride reaches just about the right balance for most conditions.It's firm enough to limit cornering roll yet sufficiently absorbent to iron out our pock-marked road surfaces.

Obviously, 4WD is standard and the handling dynamics are near neutral. Inevitably, with a tall heavy vehicle, ultimate cornering is limited by the laws of physics, suffice to say that few owners would ever want for greater adhesion or enhanced dynamics.

AN eight-speed automatic gearbox with steering wheel paddles nicely complements the performance and makes for effortless progress. Gear changes are silk smooth - it almost second-guesses the driver's intentions.

As said, economy is a surprising strong point. Our test average of 41mpg was impressive, although it dis fall short of the (unattainable) official figure of 313.9mpg.

The cabin follows BMW's well tried and highly praised design. It impresses as beautifully built and finished. It's a comfortable five-seater with ample head and legroom. A seven-seater with a third row of seats isn't offered.

The boot itself has quite a high platform but the tailgate splits to allow a small lower section which folds out to aid loading or becomes a useful seat to perch on if picnicking. Space is more restricted in the hybrid version due to the positioning of the electric gubbins - it can still absorb up to 500litres of cargo though.

While there's clearly no shortage of space within the smart cabin, there's a dearth of flat surfaces that families find useful in everyday usage.