IN its many different guises BMW's 3 Series has to go down as one of the automotive world's most versatile and adaptable all-rounders.

It's a car that has always come in multiple guises - as a saloon, an estate, a coupe and a convertible.

Only now BMW has broken up this happy little family offering something for all by creating a sub-family for the coupe and convertible versions.

Now known as the 4-Series Convertible they occupy a separate niche in the ever-expanding BMW family.

Quite what the thinking is behind this I don't know - presumably it's just designed to set them apart - but all are still based on the same 3 Series platform.

Perhaps the most revolutionary development the eternally popular convertible version has undergone in recent years has been the replacement of its traditional fabric roof with a folding metal one.

I always thought it was kind of odd that less prestigious manufacturers like Peugeot opted for this kind of technology long before the likes of BMW - but having gone for it with the last 3 Series convertible BMW has clearly decided to stick with it.

There are advantages and disadvantages as far as folding metal roofs go.

First and foremost, if they're well designed they look great when they're up.

A downside of convertibles generally is that a fabric roof can sometimes look like an ugly accoutrement, almost as if a tent's been put on top of the car.

Metal roofs also offer better protection from the elements, enhance refinement and limit road noise. The problem is that they impinge on available boot space and add a considerable amount of weight.

Design-wise the 4-Series Convertible is spot on. The convertible doesn't look all that different to the hard-topped coupe with the roof up and it also looks great with the roof down.

Simple and stylish in some respects, it's a look that works well and is also one that will no doubt age well.

The roof folds up and down reasonably swiftly and effectively - taking around 20 seconds - and can be operated at speeds of up to 11mph.

Not surprisingly boot space is limited when it's folded down (220 litres), though with it up there's a generous amount of room (370 litres). It also has an electric system to lift the folded up roof out of the way in the boot, making it easier to load items underneath it.

Is its limited boot space with the roof down a big drawback? In all honesty probably not. It just means if you're off to the south of France on holiday you'll have to wait until you get there before enjoying that roof down experience.

The mechanism is quite heavy though, adding around 215kg to the weight of a 420d SE coupe, though on the plus side this car is lighter than its 3 Series predecessor. It is also lower, wider and longer than the car it replaces.

On the inside it is nicely done out. BMW's current instrumentation and dash styling might not be to all tastes, being simple and spartan rather than snazzy but quality is evident throughout and the once awkward and hard-to-fathom iDrive infotainment system, which comes as standard, is well-designed and easy to use.

The seats are comfortable, rear seat passengers are well catered for in the space stakes and in pretty much every respect it adheres to the high standards of excellence set by BMW.

There are five trim levels to choose from, starting with the SE and in addition to this 2.0-litre diesel there are 2.0-litre and 3.0-litre petrol engine options.

The diesel is smooth and capable and obviously the preferred option when it comes to reasonable running costs.

In terms of handling, the extra weight might mean it isn't quite as sharp as a regular 3 Series equivalent or the 420d SE but compared to most ‘normal' cars it still shines.

It's at its best in the sport plus mode - one of four which also include eco pro, comfort and sport. Those optional driving modes are another added strength - particularly on a manual which often doesn't have the multiple settings offered by automatic equivalents.

I certainly found it fun and engaging to drive, even if at times one was conscious of that extra weight on board.

Any shortcomings however are perhaps compensated by ride quality that is exemplary, suggesting that this convertible has primarily been created to be a comfortable cruiser, rather than something that's designed to be chucked around corners at high speed.