Anyone still wondering what drives fashion these days need look no further than Stella McCartney’s show yesterday. It’s the shoes, baby. When a vegetarian designer comes up with non-leather accessory ranges that cut it with fashionistas it’s a safe bet that she didn’t do it for the sheer pleasure of seeing how far you can go with a piece of faux sheepskin.

McCartney knows that shoes are about the biggest fashion statement a woman can make right now. Hers are patent wedges – either ankle boots or court shoes – or knee-high boots made from something that looked like sheepskin but can’t possibly have been.

Whether the ethical aspects of PVC and fake skins outweigh the environmental side is moot, but she’s not the only high-profile designer giving materials that used to be the stigmata of the poor a luxury gloss.

The definition of luxury is up for grabs, particularly now that Tesco sells cashmere jumpers for under £20. Does “true” luxury become ever more recherché – the solution favoured by Italian designers in the headlong flight into exotic skins and triple-bonded cashmere? Or does luxury focus on originality?

McCartney’s clothes, truth be told, are often simple: a loose, dusky-blue, velvet tunic with butterfly sleeves and a ripple of ruching at the back, big fluffy wrap cardigan coats, loose, drop-waisted dresses with puffball hems and the ubiquitous black, strapless minidress. The boiled wools and textured cocoon-shaped coats occasionally tipped from interesting to matted-looking. Then again, matted is big next winter.

With the exception of the strapless minidress, these are clothes that – in the best possible sense – bring to mind evenings at home in a draughty old farmhouse with only the TV for warmth. But perhaps that’s McCartney’s life these days. They’re not sexy in a predictable way. Yet there’s clearly something alluring about a woman who feels comfortable in her clothes and sufficiently relaxed to let her shoes do the talking.

Valentino was never confused about luxury. For him it was always the finest, costliest-looking fabrics and impeccable cutting. His successor, 35-year-old Alessandra Fachinetti, has the formidable task of taking over following his retirement after 45 years. It’s extra daunting, because she was given the same challenge at Gucci. After Tom Ford left in 2004 she produced a satisfactory first collection but floundered when it came to moving things on. She was fired a year later.

Yesterday Fachinetti produced a more than satisfactory first collection – drawing on Valentino’s bountiful archives, and serving up his beloved tulip-shaped skirts, cropped military-lite jackets, lacy chiffon blouses and a handful of strapless, high-waisted evening dresses with unimpeachable tailoring and a new, youthful lightness that should keep existing customers of all ages happy. But Fachinetti’s big test will come when she tries to reinvent Valentino for a new era.

Luxury could be a very high-spec pair of trainers. So Puma announced yesterday that Hussein Chalayan (he of the dress that turns into a table) is to become its creative director. As a reaction to adidas’s successful collaboration with McCartney, it may be a clever move. Chalayan is the ultimate techie designer. The collection he showed for his own label in Paris this week featured the usual electrodes – this time wrapped round models’ waists. I think what was intended was a statement about mankind’s self-destructive tendencies. The concept was human evolution (translation: Flintstone-type jewellery at the start, pretty black silk dresses in the middle and a finale of what looked like the latest in suicide-bomber fashion statements).

Sometimes it’s best to leave the concepts on the drawing board.

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