The BMW 3 Series is not so much a range of cars as a statement of intent. While an ever-increasing number of models may swirl around the peripheries of the marque, the 3 Series has been BMW's rock-solid nucleus since 1975.

If a Martian fell to earth and asked what a BMW was, an introduction to a 320d would be all an alien species would need to understand the essence of the brand. Which is why BMW may feel free to play fast and loose with some of its more, eclectic, niche models, but never with the 3 Series. It must simply be as good as it can possibly be.

Which is not to say BMW is unaware that, even within the bedrock, some flexibility can reside. On the contrary, when you have a commodity as universally respected and revered as the 3 Series, you want to make sure that asset is exploited to the very limit.

Which is why, when the Three was first launched, there was only a two-door saloon; today, there is a saloon, estate and that curiously shaped 3 Series Gran Turismo hatchback. In the meantime, the long-serving coupé and convertibles have now been rebadged as the 4 Series, but underneath it all it’s still the same car.

But amid all this brand manipulation, one key quality has come to characterise the 3 Series, almost regardless of which model is under the microscope: class leadership.

The current ‘F30’ generation continued Munich’s best traditions of outstanding performance and rear-drive handling. It also went straight to the top of our road test class rankings – where it stayed until very recently. But with an increasingly popular Mercedes-Benz C-Class, an all-new Audi A4the vivacious Jaguar XE and the return of Alfa Romeo in the shape of the Guilia, the 3 Series needs to move forward just to stand still at the moment.

In fact, standing still may not even be a guarantee of success. Thanks to the introduction of the 4 Series line and the demise of the 3 Series Coupé and Convertible, BMW’s wider 3 Series brand has undoubtedly lost a bit of its old lustre and quietly dropped out of the UK’s top 10 biggest-selling cars.

Which may partly explain the lengths to which BMW has gone with this unusually far-reaching mid-cycle update - there’s clearly a consolidation job to be done. And this is not just the usual headlights-and-bumpers revision – although new optional LED headlights and reshaped bumpers front and rear are included in it.

New turbocharged petrol and diesel engines come in under the bonnet, coupled to an updated optional eight-speed automatic gearbox, while extensive changes have been made to the 3 Series’ suspension, cabin and equipment. The first part of 2017 also saw BMW give the 3 Series a minor refresh, with the latest version of its superb iDrive infotainment system being fitted.

But none of us must ever assume any car’s position at the top or bottom of the class. When it comes to assessing a new product, the past is irrelevant. The only question in need of an answer is how the 3 Series stacks up as proposition today.

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