VOLVO is continuing with the electrification of its model line up with the introduction of more plug-in hybrids and 48-volt diesel electric engines.

The Swedish car maker has just become the first automotive company in the world to offer plug-in variants across its range and it is now adding more eco-efficient models with its new B4 and B5 mild-hybrid powertrains.

Currently the XC60 SUV is the most electrified offering in the Volvo portfolio - although it will soon be joined by the latest and larger XC90 - and comes with all three power choices alongside conventional combustion versions.

We have just tried out all three and each has its own characteristics.

The T8 plug-in is undeniably quick and is the fastest of all XC60s. It uses a 2.0-litre petrol engine to power the front wheels and an electric motor to drive the rear.

As such, it is four-wheel-drive and with a total power output of 390hp plus a hefty 640Nm of torque it can manage to complete the 0 to 60 sprint in 5.2 seconds - not at all shabby in a vehicle weighing more than two tonnes.

Where the plug-in technology scores is with its economy and we saw an average of 63.9mpg on a brisk drive through the Cotswolds.

Officially the PHEV - or Twin Engine as Volvo calls the set up - is rated at between 94.2 and 122.8mpg under the new WLTP testing programme and emissions are as low as 47g/km which results in considerable tax savings for both private and business users.

For company car users XC60 T8 has a benefit in kind rating as low as 16 per cent while on the private front its first year road tax rate can be zero.

The car we sampled was in top grade Inscription trim and priced at £63,780 although the plug-in technology can be had on models costing from £56,955.

A variety of drive modes are available to get the most out of the powertrain and the XC60 T8 can run purely on electricity for around 30 miles. A recharge takes about three hours from a home charger.

Compared to other versions of the XC60 the electrical gubbins used on the T8 have resulted in slightly less boots space and a smaller fuel tank - but there is still more than 15 gallons to go at and luggage capacity is down by a small suitcase to 468 litres, more than enough to satisfy.

The other main difference is towing weight which is down to 2.1 tonnes braked from the 2.4 tonnes limit of the new mild-hybrid diesels.

Both the B4 and B5 versions of the XC60 replace the previous diesel only all-wheel-drive D4 and D5 models and leave the only ‘pure' diesel in the range as the front-wheel-drive D4 which now costs from £38,715.

Volvo has revised the XC60 line up to incorporate the new hybrids so exact price comparisons are not possible but the B4 is around £3,000 more expensive than its non-hybrid predecessor.

The more powerful B5 set up is available only from higher specification R-Design trim upwards and costs from £45,985 compared to £45,135 before.

Both exhibit much more life on the road and the B4 in particular gets a power hike taking its output up to 197hp.

That shaves a whole second off its 0 to 60 acceleration time at 7.8 seconds and its fuel economy ranges from 39.2 to 46.3mpg with emissions of 151g/km.

We managed to average 35.1 to the gallon from the B4 and 41.9 from the B5 which too is quicker through the gears at 6.7 seconds 0 to 60.

Officially the B5 - which has 235hp to go at - is rated the same as the B4 yet in the real world proved a little more fuel efficient.

Like for like the mild hybrid models give the diesel XC60 much more zest and are nicely sporty to drive.

The 48-volt system is currently being developed by Volvo for its petrol engines and those are due to arrive later in the year.