The all-new BMW X1 is the fourth member of BMW's 'X' family - joining the X3, X5 and X6.

It breaks new ground for BMW with an all-diesel engine line-up and rear-wheel-drive offered for the first time on an 'X' car.

Is it up to the job? Expert guide editor Keith Collantine racked up 900 miles in an X1 to find out.

They call it the BMW X1 but this isn't a jacked-up 1 series. The underpinnings of BMW's new SUV match the 3 Series, so it's noticeably larger than the 1 series in every dimension.

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A large and upright front grille, squared-off wheel arches and chunky fog lights give the X1 a rugged look.

But a close look at the underside of the car reveals black trim designed to give the impression of high ground clearance - but it is not intended as a bona fide off-roader.

Once you banish thoughts of bouncing through muddy fields from your mind and treat the X1 as what it is - a super-sized 3 series - it starts to make sense.

Impressive economy

Correctly anticipating that most X1s will spend more time near schoolyards than farmyards, BMW are offering with four-wheel-drive only as an option.

Plump for the two-wheel-drive version (that's rear-wheel-drive, naturally), and you'll benefit from reduced weight and significantly superior fuel economy:

In BMW parlance, 'sDrive' is rear-wheel-drive and 'xDrive' is four-wheel-drive.

The other point you'll notice from that table is that there are no petrol engines available. BMW's reasoning is entirely logical - well over 90% of X models are sold with diesel engines in Britain.

BMW's Efficient Dynamics technology means the X1 returns some impressive efficiency figures given its size. The smartest of these is start/stop, which automatically cuts out the engine when you put the car in neutral and raise the clutch. Depress the clutch and the car instantly fires into life again, having saved precious seconds of wasted fuel.

Steers like a saloon

We tested the mid-range 23d with a six-speed manual gearbox. Over nearly a thousand miles of B-roads, A-roads and motorways the X1 felt more like a saloon than an SUV at every turn.

A touch more body roll than its smaller siblings gives away its heftier size. But it rode very smoothly, partly thanks to the use of conventional tyres rather than BMW's preferred run-flats on our car - a setup that's better suited to Britain's harsh road surfaces.

However if you want to upgrade from 17 to 18-inch rims you'll have to have run-flats, with a likely loss of ride comfort.

The bluff front of the car doesn't cut through the air as cleanly as you'd like, giving a little wind noise though only at motorway speeds.

The interior is the usual BMW fare - our base specification model came with only a few upgrades but the dashboard and trim felt well-built. However there is a generous supply of cup holders and power sockets.

Most of the equipment is straightforward to use, except the aircon, which proved difficult to discourage from blasting a high volume of air at you and was slow to change temperature.

With all the seats in place, rear luggage space is slightly disappointing at 420 litres. They fold flat quickly and easily, however, giving 1,350 litres of storage, and they split 40-20-40.

Our X1 had the 'extended storage' option (£105 extra) and the luggage compartment separating net (another £105). Large rubber tie-downs in the boot were especially useful for keeping luggage from sliding around.

In the cabin you get a high driving position with a good view of the road around you. Unfortunately the generously-sized wing mirrors can obscure visibility at junctions.

Few rivals

BMW's premium rivals Audi and Mercedes are both thought to be working on similar-sized cars to the X1 but they are some way off.

With the Range Rover LRX not due for before 2011, the X1's closest rivals in the meantime are the Volkswagen Tiguan, Nissan Qashqai, Ford Kuga and Toyota RAV 4.

Only Volkswagen comes close to having the brand appeal of a BMW, and that combined with the X1's superior power and fuel economy should seal the deal for the many prospective buyers BMW hope to capture.

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