ALREADY the Volvo XC90 has been recognised as the safest car on the planet and now it's notching up another milestone as the world's first seven seat plug-in hybrid.

With an electric motor added to its existing super-boosted petrol engine it can pump out a mighty 407 horsepower resulting in stupendous performance statistics.

How does 0 to 60 in 5.3 seconds and a top end of 140mph sound for a king-sized SUV that weighs in at the best part of 2.3 tonnes?

But the clever bit comes with fuel economy and the new Volvo XC90 T8 Twin Motor - as this hybrid is known - has been rated at an incredible 134.5 miles per gallon with CO2 emissions of just 49g/km.

A must have and worth every penny of the £63,355 it costs for the mid-grade R-Design model we tried?

Well if you think this futuristic powerhouse is going to save you thousands at the pumps then unless you cover only a handful of miles a day, think again.

Where the real benefits of a plug-in hybrid lie are with the taxman and for business drivers the XC90 T8 is worth its weight in gold.

Every penny of the purchase price can be written off against tax in the first year, the R-Design qualifies for £12,550 in Corporation Tax relief and its benefit in kind charge is only five per cent which in itself reduces National Insurance contributions.

Stacked against a conventional model of a similar price that adds up to a hefty amount of hard-earned cash that won't be going to the revenue - and there's no road tax to pay.

Moreover, if you live in London, this XC90 escapes the congestion charge and regardless of your address it comes with the right amount of prestige.

In base level Momentum trim the XC90 T8 costs from £60,455 and top grade Inscription models start from £64,205 making the plug-in some £14,000 more expensive than diesel versions and around £10,000 more than the petrol only XC90 T6 which has the same 2.0-litre Drive E engine as the T8 but without the electric power hike.

There is no question about the XC90's driving abilities and the dual power sources of the Twin Engine T8 see an electric motor hooked up to the back axle to supplement the 320hp turbo boosted and supercharged four-cylinder engine at the front.

Together the power is astonishing and can give the T8 a real punch under acceleration yet a multi-mode drive control allows for plenty of flexibility.

As a purely electric vehicle Volvo is claiming the T8 has a maximum range of 27 miles but it can be set up to run as a hybrid using both petrol and electric motors in normal or sporty settings or combined to give maximum traction in an all-wheel-drive mode.

There is also a setting to conserve battery power enabling the T8 to be switched into EV mode later in a journey - so cruise conventionally then drive as a zero emission vehicle in town.

Top speed when running purely on electricity is 78mph and even in full 4x4 set up it can top the ton.

The lithium ion battery pack can be fully recharged in two-and-a-half hours from a fast charging point or between three-and-a-half and six hours from a domestic supply and the T8 has an 11 gallon fuel tank - 5.5 gallons smaller than that of the non-hybrid XC90s but enough to give it plenty of range.

Regenerative braking will replenish the battery on the go but we managed only to add a couple of miles to the available range.

On our drive the car was showing an EV range of just 13 miles on start up and after a regular journey in hybrid mode returned an average of 36mpg over 60 miles - a huge way off the official figure but almost 40 per cent more than you could expect from a T6 in similar conditions.

That's the rub with every plug-in vehicle. Incredible technology it may be but it's all down to how it is used and for high mileage drivers a diesel remains the better bet.

However, in the plug-in world Volvo has hit the mark in many a way with the XC90 T8 Twin Engine and unlike other PHEV SUVs from BMW and Mitsubishi, the Scandinavians have pulled off the transformation without compromise.

Siting the battery pack on the XC90 between the front seats means there is no impact on cabin space and allows the car to retain its seven seats and all of its luggage capacity.

Additional features on the T8 include air conditioning for all three rows of seats, a panoramic sunroof, a 12.3-inch TFT instrument panel and a typically Swedish touch in the form of an Orrefors crystal glass gearlever.

The instrument panel can be set up to give a number of displays including navigation instructions and the virtual dials are modified on the T8 to show electric information such as the state of battery charge.

In R-Design trim there are extra body features such as a restyled grille finished in gloss black, trim touches inside and twin exhausts at the rear.

Those are on top of the fixtures and fittings which have won the XC90 plenty of plaudits since it first appeared last year such as its high tech, tablet-style touchscreen, its luxuriously appointed interior and the extensive connectivity and safety systems which saw the vehicle grabbing top spot in the Euro NCAP crash test programme as the safest car around.