Well now I know. It's because they can. We may all pretend to be happy enough with our affordable practicalmobiles but is there anyone who would turn down the chance to own something big, in your face and posh. No, I didn't think so.

Why? Because they are lovely and when you live with them for a while you realise they are great too and not just for show.

Take the BMW 730dL for instance.

That's big, in fact it's massive, the 'L' denoting long wheelbase. It's also luxurious with acres of leather, loads of toys and even a couple of televisions front and back.

Lucky backseat passengers can even watch DVDs or satellite telly while on the move and they can stretch their legs out in comfort, resting them on the couple of footstools lurking below.

The 730d is extremely powerful, with 231bhp coming from the 3.0 in-line six cylinder turbo diesel. It will crack 60mph in 7.8 seconds and go on to more than 140mph, where conditions permit ie abroad. More important is the 520Nm of torque that floods seamlessly into play making it a great car to use cross-country.

Despite its huge proportions the big Seven is amazingly easy to drive in town and on the open road. Parking is no problem thanks to sophisticated parking sensors and a graphic that appears on the dashboard screen that turns from green to red as you approach an obstacle.

In true BMW fashion, the car also handles superbly and in a way that belies it size. Braking is phenomenal and handling secure so safety is never an issue. If things do go awry then the electronic wizardry kicks in to sort it out.

The six-speed gearbox can be left in full automatic or you can play around with gear-change buttons on the steering wheel.

The upshot of all this is that when you are harassed, stressed and drowning in work, the 730d helps take the strain. It relaxes where many motors frustrate; it provides an oasis of calm in the desert of mayhem that has become our daily lives. It contributes hugely to the quality of your working life and really should be available to everyone on the NHS.

So next time someone floats by in a big executive motor, do feel free to be resentful as the car probably is as good as it looks. The 730dL certainly is.