WHEN it comes to combining luxurious comfort with electric performance, BMW has few peers.

But now the firm has taken that electric performance further, literally, with a big push in diverging from the combustion engine alone technology.

Take that technology and add it to one of its most enduring models, the X5, and this plug-in version and you have a vehicle that has literally electric performance together a massiveeconomy and ultra-low CO2 emissions.

In this case the vehicle has a claimed theoreticl economy of a 180-230-odd mpg combined with just 31g/km of CO2, producing massive savings on the day to day running of the vehicle, particularly for business users.

BMW claims it can travel up to 54 miles purely on electricity which means on the company car tax scale - for PHEVs now calculated on electric range as well as overall emissions - that its benefit-in-kind rating is just eight per cent.

Of course the mpg is theoretical unless you are driving less than the electric range miles and are charging the car every day and with very little use of the three-litre V6 twin turbo-charged petrol engine. It would seem obvious, however, that drivers would wish to make use of all that pace and power at some point.

The X5 is now in its fourth incarnation and this model has produced a combined system power output of 394bhp, 286bhp augmented by the 112bhp from the battery.

It feels jet propelled and can hit 60mph in around five-and-a-half seconds and on to a top speed of 146mph. Even in electric only it can hit an impressive 85mph.

The engine is combined with the 82kW lithium-ion extended storage battery to provide the power needed to shift a 2.5 tonne vehicle so quickly and so economically.

It also combines the BMW EfficientDynamics drive family and the super-slick, eight-speed automatic transmission with the latest generation and the intelligent all-wheel on-demand xDrive system.

There are various drive modes, which are selected by buttons near the gear shift, with electric, hybrid, sport and auto adaptive available. Obviously for maximum economy choose electric and for serious fun, choose sport and let rip by using the steering wheel paddles, but for most, the auto mode will select drive mode for the appropriate conditions.

In addition, the vehicle's smart route navigation and can keep electric power in reserve for urban driving later in the journey.

A separate Battery Hold mode and regenerative braking, allows the battery to be fully charged while driving. On top of this, a 69-litre fuel tank also ensures fewer expensive visits to the filling stations.

The X5 has always been an attractive motor, but in the M Sport mode it really does look the business with its slim headlamps, huge, diamond cut alloys and the familiar kidney grille, air scoops and side air vents finished in gloss black.

The interior is pure class, a riot of leather and high end soft touch finish. It is a big car with plenty of head and legroom at the front, although the rear is more limited. It offers a raft of hi-tech, high end bells and whistles that you would expect from a £66,000-odd motor, including head-up display and electrically heated and powered front seats.

The M Sport model also includes a sports steering wheel, specific pedals, driver's footrest and piping on the seats, plus exclusive interior trim in aluminium. Also included on this model adaptive air suspension, 20-inch alloy wheels.

Central is the 12.3-inch touchscreen in the middle of the dash with controls sat nav, infotainment and connectivity and climate control controlled by the now familiar iDrive rotary dial on the central console. Connectivity includes Apple CarPlay, digital radio, enhanced Bluetooth with wireless charging and gesture control.

On the road, the two-axle air suspension and electronically controlled dampers makes for a smooth and controlled ride with sharp, agile handling and a comfortable ride for all passengers, although it became unsettled over larger potholes and bumps.

It remains a practical vehicle and when all seats are used, the storage volume is 500 litres. Fold the rear backrests and a cavernous 1,720 litres is available. A two-section tailgate for ease of loading with optional remote opening and closing.

Safety kit is comprehensive, with full complement of airbags, traction and stability control plus, plus lane change warning, crossing traffic warning, rear-end collision warning and speed limit information.

Another key feature for electric cars is when the vehicle is running at low speeds on electric power, a speaker system emits a distinctive sound generated to alert pedestrians.

At more than £66,000, it's not cheap, but considering it has a three litre petrol engine on board, running costs are good.