YOU know a car is important to its maker when the first 25 pages of the info pack for road testers is all about the vehicle's heritage. Only then do you arrive at today's machine.

Which in this case is the latest version of the car that means perhaps more than anything to BMW - the 3 Series.

More than 14 million of them have been sold since the first one appeared as a modestly sized sporty saloon in 1975.

Today, around one in four BMWs sold around the world is a 3 Series. So its continuing success, against ever stronger opposition (Jaguar's XE is the latest) could not be more important for the Bavarian car maker.

And that means you tinker with the basics at your peril. Much more sensible to advance in small steps, making successive models a bit faster, slightly more economical and making sure there are enough versions to tempt the maximum number of potential buyers.

Which, in the case of UK 3 Series buyers, means at least 112 different types to consider, from modest rear-wheel drive petrol models to big diesel bruisers with all-wheel drive and enough attitude to take pole position in the company car park.

That's before you take in the list of possible options. Always a German car maker's speciality, you can go crazy with the tick boxes and end up with something like the car on test.

It was laden with an extraordinary £12,010 worth of options. Decide that after all you could live without a front armrest with sliding adjustment and already you've clawed back £45 (and every little helps).

You don't of course, have to take any of the options, although you won't see many 3 Series without metallic paint (£645) and heated front seats (£325) ought to be standard.

But back to the car itself; put it next to a just superseded version and you'd need to be a BMW anorak to spot the difference. Tiny changes to air intakes and lights are the signs, while inside you might spot a bit of high gloss black - and cup holders with a sliding cover.

Under the bonnet all the petrol engines and most of the diesels are new to the 3 Series, with useful gains in economy and emissions the result.

BMW knows it has to maintain its reputation as a maker of cars with a sporty feel and its engineers worry about the details, to the extent that the front suspension now uses five bolts to hold it to the body instead of three. That means less distortion and a purer feel when you're pressing on.

Which you may want to do in a car like the model on test. Slipping into the hip-hugging front seats (a part of the £2,500 you pay for the M Sport package) you know instantly that BMW sweats the details.

So the pedals are in precisely the right place, the instruments big, bold and easily read and there's a general air of sober sense and lots of well applied black.

You might find the stiffened suspension a bit grumbly over poor road surfaces but the poise and balance of the car is compensation enough.

The eight-speed automatic gearbox comes into its own when you feel less like a potential F1 entrant - perhaps on the way home after a hard day at the office when nothing went right.