YOU really do need a degree in accountancy before signing for a new Q7 e-tron from Audi, unless the thought of near silent travel for mere pence is more than enough to clinch the deal.

This SUV is big (and bold, with a radiator grille a medieval knight would fancy for battle armour) and comes with built-in attitude and some off-road prowess.

It is the second car in the Audi range to be given an electrical boost.

The first was the much smaller A3 e-tron and both use the same thought process; add an electric motor to a conventional power unit (a stonking 3.0 litre turbo diesel in the case of the Q7) to give some miles of almost free motoring before the ordinary power unit kicks in.

Just as important - or much more important, probably, for the vast majority of people running a Q7 e-tron on a business account - are the tax savings to be made from wearing your eco heart on your eco sleeve, with a mere five per cent BIK charge and so little tailpipe pollution (48g/km) that you'll laugh at road tax and congestion charges.

There has to a be a sting in the save money argument, you're thinking. And you are right; Audi bases the new part-electric Q7 e-tron on a SE spec car and pops a not inconsiderable £13,220 premium on top. That brings the bottom line to £64,265. That sounds quite a lot.

You don't have to be much of a numbers person to work out that you could buy a lot of diesel for that princely uplift, ditto a lot of visits to the London congestion zone and a lot of tax discs - I know they don't issue them any more, but you get the point.

Talking numbers, Audi reckons a full charge of an e-tron battery, taking a bit more than two hours via a dedicated charger or eight hours from a domestic socket (i.e. in the garage overnight) will power the Q7 e-tron for 35 miles before the 245bhp diesel is asked to join the party.

Those 35 miles, especially if enjoyed around town, will be an almost out of body experience. Without wind noise or tyre roar (remember we're doing no more than 30mph) the big, plushly leathered Audi moves as though someone had turned the sound right down to almost off.

Combine this extreme aural hush with air springs that provide a near boulevard ride and you have a car to impress heads of state or catwalk stars on their way to the next summit meeting or movie premiere.

Should you break free of urban restraint the car will hit 84mph flat out on battery power alone, but don't expect to go anything like 35 miles at those speeds before needing diesel back-up. With the conventional engine helping, the car will then hustle to a top speed of 143mph.

Acceleration is snappy whatever power source is engaged at the time, with 62mph reached in 6.2 seconds with the diesel working or a scarcely slower 6.5 seconds on pure electric urge.

The battery adds a whopping 202 kilos to the weight of an already chunky machine, taking it to 2445kgs before anyone steps on board. That will have consequences on fuel consumption, although the daft rules Audi must follow simply do not take a real world view of economy.

The company quotes an extraordinary 156.9mpg in the official Euro test and must hope the new more realistic test regime we are promised from Europe arrives soon, in time to stop cynics laughing any longer at the figure.

The car itself is no laughing matter. If it makes sense to both yourself and your accountant, you are unlikely to be disappointed with this gentle giant.