Conventional wisdom has it that even the best of ideas can be stretched only so far before it breaks.

BMW, in the form of the ever-extending Mini family, seems determined to test this theory. The Mini, reinvented in 2001 and built around the Cooper core now extends from a basic petrol model to take in diesels, convertibles, estates and, even, a 4x4 on the way to the John Cooper Works sports model.

The JCW sits at the top end of this elastic brand and has itself been extended this year with the addition of a convertible. This super-charged, super-stylised JCW goes a large step beyond the already punchy Cooper S, its 1.6 litre engine pumping out 211 hp, allowing it to zip from 0-60 in 6.9 seconds and crank out a top speed of 146mph.

With the lid down this exhilarating performance is, literally, hair-raising. Naturally, the British weather conspired to offer few opportunities to go topless but it did not matter as the JCW’s main asset is under the bonnet.

Due reverence to Alec Issigonis, designer of the original Mini, and one of his defining principles – a wheel in each corner – assures that, in spite of its power, the JCW sticks to the road like chewing gum to the shoe. My son, after a trip in the car, could not understand why his Scalextric Cooper kept flying off the track when the real thing was so much more sure-footed.

Such performance takes the JCW out of the hot-hatch arena and into the world of the sports car, but at a very affordable price (£23,475). BMW chances its arm in this respect by tacking on various grills and spoilers that are, almost entirely, intended to add to style rather than performance, as most serve no function at all.

Crucially, however, the JCW avoids the charge of tackiness because it is still, demonstrably, a Mini. It retains the marque’s quirky charm and character – a quality often claimed by motor manufacturers for their (normally boring) vehicles, but truly applicable to the Mini. The retro interior, the chunkiness, the curves are all still there but the JCW adds an edge – this is the angry teenager of the Mini family complete with a growl, in the form of throaty exhaust.

For all its extra aggression, the JCW is a fairly conventional addition to the Mini marque. The Clubman is far more of a stretch – in every sense of the word.

The original Mini Clubman was a strange invention of what was then British Leyland. As far as I can remember, its main difference from the standard Mini was that it had square headlights and go-faster wheels.

The new Clubman is a reinvention of the old Mini estate. The body is lengthened, it has the twin, van-like doors for access to the boot space of the original and, most ingeniously, a small third side door allowing relatively easy access to the rear seats.

This small door encapsulates the appeal of the new Mini. An outwardly mundane and practical element evokes wistful memories of childhood as, 30 or so years ago when I was but a boy, my Dad would occasionally drive us all (parents, four children) from Southampton to east London in a Mini borrowed from work. On one such occasion, as we negotiated the Chiswick roundabout smoke began to billow out of the steering column. Dad immediately pulled in to a garage and no six people have ever got out of such a small car in such quick time.

The Clubman is an expression of BMW’s confidence in the Mini brand. It’s as if the company has taken pity on all those poor parents who, by virtue of the two-legged baggage they have to carry, are locked out of the main Mini market. The Clubman is their opportunity to join the fun.

The confidence is well-placed. The Mini shows no sign of falling victim to its success as the car’s ubiquity seems only to enhance its appeal, an appeal that has even survived its association with estate agents and hairdressers. Next year, the family is to grow again with the edition of an electric Mini, the 15th reinvention of an idea that is only gaining in strength.

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The details

Say hello to: teenage kicks

Say goodbye to: loosely attached hats, wigs, children

How fast?
0-60 in 6.9secs, 146mph

How thirsty?
39.8mpg combined

How green?
169g/km

How much?
£23,475