I'm in a minibus and the view of the road through the front screen has just been replaced by bright blue sky. Normally that would signal something is very very wrong, an accident only tenths of seconds away and it's all going to end with an incredibly loud noise. Thankfully I'm not responsible for any passengers today (the seats behind are all empty) and instructor Howard remains resolutely calm, despite sitting right next to me.

It's not because he's asleep either, he's seeing the same sky I am, but this is all completely normal and expected - in fact it's all in a day's work for him. You see this is no ordinary minibus, this is a Mercedes-Benz Sprinter 4X4 minibus and we're mud-plugging our way around the Millbrook proving ground.

It's a strange beast, and one that will prove to be a rare sight in the UK, representing less than one per cent of the total Sprinters delivered here. From the outside it looks exactly like any other, save for the 40mm increase in ride height. The result on our high-roofed people carrier (you can specify the 4x4 drivetrain across most of the range) is a van that stands over three metres tall, and less than two metres across. More topple-over-tall than super wide in stance then - think mountain goat on wheels and you've probably got the picture.

Underneath the panel van body there's an electronic traction system (4ETS) fully integrated into the ESP. Doing without the traditional mechanical differential locks reduces weight, and the fully automatic set up will split power 35:65 between the front and rear axle, braking individual spinning wheels and hence activating those that have the most grip. There's even an electronic low ratio gear reduction that engages automatically if the vehicle detects it's about to get stuck on its way up a steep incline.

Back to the rough stuff, and that sky-filled screen for a moment though. The Sprinter continues its possessed animal impression and scrambles to the very summit of the hill we're on with relative ease. Rolling gently over the top, the blue is suddenly replaced with varying shades of green and brown, and I cover the brake and start our descent. Without a set of dedicated low-range ratios, gentle application of the middle pedal is needed to bring the speed down to a reasonable pace, especially when approaching the bottom where the surface levels out - hitting this too quickly could result in a very bashed Mercedes badge.

Seeing it do all of this, or worse still, experiencing it from one of the rear seats, is 100 per cent uncomfortable. Eyes closed in trepidation of tipping over, you're especially aware of just how unstable this package should be. However, from the driver's seat there's no sign of such worry, and you soon forget that behind you is such a long, narrow and tall vehicle. To think you could do it with 10 passengers on board is even more of a giggle. Laughter aside though, despite the apparent lack of composure and sure-footed grip, the Sprinter simply shrugs it off and moves on to the next obstacle.

Show it some of the more challenging lumps and bumps and you'll notice the impressive axle articulation, happily lifting a wheel as the other is compressed into the opposite arch. From the cabin you're aware of vibration and noise from the engine bay as the 4ETS does its stuff. Progress is momentarily slowed, but a gentle application of power (the system only works when it can detect slip) soon has the drive transferred to the wheel with the most grip, and the Sprinter claws itself forward once again.

There aren't many vehicles that can carry 10 people while doing all this.

Key Facts

Model tested: Mercedes-Benz Sprinter 315CDI Medium TL9 4X4
Pricing: £31,540 (£42,240 as tested)
Engine: 2.1-litre turbocharged four-cylinder diesel
Transmission: six-speed manual, four-wheel drive
Body style: 10-seat minibus
Power: 148bhp at 3,800rpm
Torque: 243lb.ft at 1,200rpm