We return to that curious automotive phenomenon, the off-road four wheel drive vehicle. These machines are designed to provide transport across rough and hostile terrain, in the same way that articulated lorries are designed to carry goods in enormous quantities and fork-lift trucks exist to move bulky objects across very short distances.

You wouldn't buy an articulated lorry in order to go carvanning in the West Highlands, nor do I know of anyone who competes in rallies with a fork-lift truck. The compromise between basic design and intended use is too great. But there is a fashion for using off-road vehicles as if they were ordinary cars, and the motor industry has had to cater for it.

The two ways of doing this are to festoon a real off-roader with leather upholstery and air conditioning and so on to disguise the fact that its on-road handling is not great, or to create something that looks very like an off-roader but actually has trouble trying to cross a wet field.

Every rule in the book suggests that the Isuzu Trooper should be a dismal thing to drive on the road. It's jolly big, and it is clearly designed with off-road capability as one of the priorities.

And yet Troopers have always been quite surprisingly capable in normal conditions. The latest generation, visually little more than a freshen-up, represents a leap forward in this respect.

The steering is sharp, the ride is impressive, and although the amount of interior space keeps reminding you that this is a very large machine, it nips along twisty country roads with scarcely credible poise.

None of this seems to have compromised the Trooper's off-road performance. Isuzu provided a route over farmland and forestry ground - not the hardest test I have seen, but probably close to what a Trooper will be used for - and even an amateur like myself found it easy. The things it can't do are the things I would be too scared to want it to do.

Big cars need big engines, and Isuzu is justifiably proud of the two options in the Trooper. The more technically intriguing is the 3-litre turbodiesel, which has narrowly squeaked in as the first production engine of its type to enter the UK market with a pressurised rail and electronic fuel injection system (passenger cars with something similar are due to appear shortly).

The upshot of this is that, instead of being splashed in any old how, diesel fuel is injected in exactly the right quantity at exactly the right time. Because this makes the whole process more efficient, there are benefits both in economy and in performance. In fact, there is enough power to make you wonder why anyone would need more.

A crummy 0-60mph time in the mid-teens shows just how inappropriate that test is, since there are other vehicles which can beat the figure but would have difficulty keeping up with the Trooper in a cross-country dash.

The 3.5-litre V6 petrol version is seriously quick, to say nothing of smooth, refined and pleasing to the ear. It is also, according to Isuzu, more economical than the outgoing 3.2, though I would prefer to drive it in areas where the petrol stations are reasonably close together.

As has always been the case, the Trooper is available in long or short wheelbase versions, and in Standard, Duty and Citation equipment and trim levels. Prices go from #19,100 to #26,650 on the road (add #1300 for the automatic transmission option), and if it does not sell well at that sort of money, I shall eat my green wellies.