We had our suspicions after the first three looks, and by half-time, they were confirmed: with her autumn 2014 show, Victoria Beckham joined the ranks of Serious Fashion Person. She had tackled, with elan, the mid-height hem – on dresses, skirts and coats - and that makes her part of an elite squad of designers.

The midi skirt is more a concept than it is a wardrobe piece – or at least it has been up until now. It has, in its history, made political statements, reflected economic climes, and been part of the war effort. What Victoria Beckham has done with it is to bundle all that heritage into something that feels commercially relevant and eminently wearable.

She isn’t the first or only designer to have revived the style – Phoebe Philo at Celine, Christopher Kane, Marc Jacobs and Riccardo Tisci have all offered interpretations in recent seasons. It has been in fashion for a while now. But its adoption by the designer-formerly-known-as-Posh-Spice feels like a cultural event.

The mid-height hem, you see, brings with it a certain gravitas. It’s at once serious, sexy and even sometimes saccharine, according to whether it’s a loose, tubi cut, a clingy pencil style or a girlish dirndl. But what it isn’t is obvious – it’s no prudish, formal full-length or look-at-me mini. It’s a considered, practical and quietly elegant length that confers a special something on its wearer. It has been, for all of these reason, something of an intellectual length, until now.

The midi skirt has its origins in the work of Paul Poiret during the the first decade of the 20^th century. Tired of women in corset, bustles and crinolines – which he described as making them look ‘as if they were pulling a trailer’ – he went on a mission to free up womenswear from Edwardian constriction. His Chinoiserie-inspired pieces went on to become some of the first mid-length skirts, those of the Flappers during the 1920s.

It was at this point that Coco Chanel picked up on the midi. Her ethos was about making womenswear practical, about finding the elegance in ease rather than in ostentation and opulence. Her mid-length skirts came in simple cotton and some were the first use of tricot and jersey in daywear (previously, these fabrics were reserved for undies).

Hem heights dropped again during the 30s, some say for economic reasons – that fiscal gloom brings with it a prudishness – but it was probably more in reaction to the excesses of the 20s, in which hems had eventually climbed to over the knee. During this decade, and the next two, hems stayed resolutely mid-height, that is, cropped to the shin, well below them.

Part of this was because of the war effort – not only was cloth in short supply but women were going out to work in large numbers for the first time, so clothing became uniform and practical. For many, this aesthetic endured well into the 50s but for a privileged few, when Christian Dior unveiled his New Look in 1947, there came a New Look for the midi skirt.

According to adage, there was outrage and exclamation at the fashions coming from Paris at that time – the full circle skirts pioneered by Dior used up so much cloth, during an age of austerity and rationing, that they were beyond the budgets of most and scandalised many more. But they set the sartorial standard for the coming ten years.

It wasn’t until the 60s that the midi-skirt began to wane as the mini took over, with the coming of that decade’s ‘youthquake’. To some extent, it was this toppling that has established it in the modern mind as an ‘alternative’ choice. Although it endured in wardrobes around the world as the sort of thing you might see old ladies and frumps wearing, it wasn’t until the 80s that the mid-height hemline became a talking point again.

The Japanese designers Rei Kawakubo and Yohji Yamamoto brought with them, when they took Paris by storm at the beginning of that decade, a new sobriety in the way they dressed women. Their many adherents were called ‘the crows’ for their all-black ensembles; their cuts were flat and de-sensualised (in contrast to the hyper-feminine catwalks of Christian Lacroix and Mugler, at around the same time) and the fit was intentionally awkward: the midi slotted perfectly into this regimen, worn with flat shoes and oversized knits.

Forty years on, and what was once the uniform of the avant garde serves as inspiration for a celebrity designer – albeit one of a calibre far higher and more thorough aesthetic integrity than that term suggests. Beckham’s autumn 2104 triumph served up deconstructed kilts worn with huge ribbed knits, all flapping around at mid-height; there were sinuous dresses that fell to the length too, and mannish Crombies cut long and lean to the body.

It felt like a Damascene moment, not only with regard to Beckham’s eye-poppingly successful career and re-invention, but also in the annals of female dress. If someone with as much mainstream recognition as Beckham is proposing styles like this – sober, sophisticated, serious – does she therefore also have the influence to change the template of modern femininity and perceived sexiness?

She’s done it herself, after all. Gone are the permatan and the boob job; off with the head of Queen Wag; those tumbling extensions are no more. For those of us tiring of naked popstars and fake-tanned reality TV stars as the public face of the 21st century woman, Victoria Beckham’s ascension to Serious Fashion Person, and the evolution of her label’s aesthetic into something both thought-provoking and with mainstream appeal, are very positive signs indeed.