THE first plug-in Range Rover is on the way as Land Rover gears up its electronic revolution.

On paper it's the first 100mpg-plus Range Rover and with emissions of just 64g/km the plug-in hybrid has immense appeal to business users.

In reality it's a bit of a gas-guzzler once the electricity has gone - expect little more than 25 to the gallon on a run - but that's going to do nothing to diminish its low tax status set by its CO2 output.

And as with any PHEV there's a variety of ways of getting more out of the Range Rover P400e on shorter trips.

Land Rover claims the Range Rover plug-in hybrid can travel up to 31 miles purely on battery power and at speeds of up to 85mph.

After that a 2.0-litre petrol engine cuts in and the Range Rover P400e operates as a hybrid with quite sporty performance.

Recharging the battery can be done in two hours 45 minutes from a fast charger - seven-and-a-half hours from a domestic supply - and there's many a way of driving this Range Rover to save energy.

It starts up on battery power but that can be saved up by switching to the petrol/hybrid mode until EV work is required.

Leave it to its own devices and it runs as an EV whenever possible to conserve fuel but transforms back to hybrid power seamlessly if necessary.

Drive it off road and there's another bonus with instant torque available from the electric motor - and on this Range Rover it is rated at 640Nm.

It is a fascinating extension to the Range Rover story and gives the world's most luxurious 4x4 an extra lease of life as it nears its 50 anniversary.

The plug-in Range Rover is priced from £86,965 in Vogue trim and standard wheelbase and tops out at £105,865 for one in Autobiography specification - and that's just £165 more than the SDV8 diesel variants.

As such, the PHEV replaces the V6 hybrid model and slots into the Range Rover line up between the diesels and the mighty V8 supercharged versions.

Long wheelbase models are available too and those cost from £113,065 for an Autobiography or £168,015 for a super-luxurious SVAutobiography.

Like the plug-in version of the Range Rover Sport the Range Rover P400e is fitted with an 85KW electric motor and a 2.0-litre Ingenium petrol engine.

Together they develop 404bhp and that's bettered in the Range Rover line up only by the supercharged V8s which have either 525 or 565bhp on tap.

It gives the 2.5-tonne hybrid surprisingly brisk performance figures of 0 to 60 in 6.8 seconds and a top speed of 137mph.

There is no doubt about its potency but once the battery is exhausted for pure EV work it is a thirsty beast.

We managed to run for 36 miles before the EV range hit zero and that was after a lengthy off-road session across the grounds of Blenheim Palace in Oxfordshire.

In every way the plug-in is just as capable as any other Range Rover - it can wade through water up to 900mm deep - and running only on electricity the instant torque is handy.

Land Rover's engineers have modified the Terrain Response traction system to accommodate the power hit and the P400e is a meaty performer in the mire.

The drive comes through an eight-speed auto box so it is hooked up to both axles in true 4x4 fashion but the 101mpg official fuel return is fanciful. We saw an overall average of just 24.2 to the gallon after a run through the Cotswolds to Broadway in Worcestershire.

The battery pack is slung below the back of the car and that has had some impact on boot space, although at 802 litres it remains huge.

At low speeds and when running silently in EV mode the car emits what Land Rover calls AVAS. It stands for Audible Vehicle Alert System and although it can't heard inside it operates at a variety of frequencies to alert everything from humans to animals - especially guide dogs - that a vehicle is approaching.

Inside, the Range Rover P400e is as splendid as any other Range Rover and comes with the latest cockpit revisions which include two large central display screens in addition to a 12-inch interactive instrument panel which is modified to show EV information such as powerflow and available range.

The Autobiography model we drove also came with a head up display, 24-way power adjustable heated and cooling front seats with massage functions and even a domestic power socket.

In every way the P400e is a car for modern times and significantly Land Rover says it is likely to account for 20 per cent of Range Rover sales in the coming months.

That is largely down to the tax advantages such cars bring to business users but for those whose daily run is within the electric range there are significant savings to be made from the plug-in technology.