There was once a school of thought that suggested wearing leggings day in, day out, was a sign of style slovenliness. An easy, comfortable but not so fashion-forward solution to the often-fraught question of dressing our lower halves. But you may have noticed that the fortune of leggings has taken a turn. Now, they are less a compromise, more a stealth statement of efficiency and casual sophistication – if you have the right ones.

Bounding around town in the sleekest, most flattering leggings now carries as much cachet as having the sunglasses or bag du jour, but because they’re such an apparently functional, sporty piece, there’s a sense of effortlessness to them that is difficult to conjure elsewhere in your look. ‘What these things? I just pulled them on in a whizz this morning, but why yes, they do give me gazelle-like grace, come to think of it,’ they seem to suggest. See shots of Sienna Miller, Jennifer Garner or Naomi Campbell doing that mysterious, yet somehow relatable, activity ‘running errands’ in theirs.

You may have noticed the leggings effect in action in your chicest coffee shop, yoga studio or at the school gates. At the latter, the new breed of leggings will put you at no risk of being asked to smarten up by the head teacher (a humiliation one school’s parents suffered when the headmistress issued a diktat against pyjamas on the school run), but rather will signify that, a) You’re so on it that you’ve already fitted in a workout around getting the packed lunches together, or b) Your post drop-off morning will consist of that miracle Pilates class everyone has been raving about. And even if you plan nothing more than a dash to the supermarket, the sofa or the office, the effect is really the same.

Fashion search engine Lyst has noted that the average spend on leggings has increased 49 per cent year on year. There has been a 29 per cent rise in the number of styles available, too – meaning retailers are creating more options to feed demand.

‘You can’t go cheap, it’s just not worth it – they are totally see-through around [your bottom],’ argues Stacey Duguid, the fashion editor behind bestdressedguest.com. ‘If you spend more you’ll have them for years. My friend wore either Fendi or Tom Ford leggings throughout both pregnancies, which sounds really excessive, but not if you think she wore them every single day for 18 months straight.’

Of course, leggings fall into two camps – the sporty kind and the trousers kind. The three most in-demand brands in the West are a mix of both: Nike, Joseph and Gucci, with The Upside and Varley (both luxe gym labels) rising fast in popularity. I can vouch for Lululemon’s Speed Ups, Sweaty Betty’s Zero Gravity or Tory Sport.

At the more affordable end of the spectrum, there are great options: Blossom Yoga Wear’s high-waisted yoga pants (which come in loud prints or muted black) and Zaazee’s Adriana contoured leggings have both passed the ‘see-through-bottom’ test for me, as do Gap’s Sculpt Revolution capris. Try sizing down for a good fit and search for a pair that hits you at the perfect point an inch or two above the ankle bone.

Another label that has perfected its leggings offering is Lucas Hugh, which was at the vanguard of the upscale activewear movement when it was founded by New Zealander Anjhe Mules in 2010. Mules is the perfect poster-woman for a modern way of approaching wearing leggings. When I met her recently, she was wearing her super streamlined Odyssey leggings with a mannish white shirt from Zara and adidas Primeknit trainers – the perfect uniform, she says, for feeling ‘tailored and not sloppy’ for days spent juggling running a business with exercise and childcare.

‘We’ve really noticed that women are more confident to wear activewear throughout the day as a key part of their wardrobe,’ she explains. ‘Previously, they might have been scared to do that, but the design features you get now make you feel powerful. We’ve developed a lot of bonding, laser cutting and high compression technology, which make the leggings an amazing fit.’

These features not only skim and sculpt to give a flattering silhouette, but can have health benefits too, as Serena Williams (who suffered blood clots after the birth of her daughter last year) attested when speaking at a press conference in May about her Nike catsuit. She said she’d ‘been wearing pants in general a lot when I play, so I can keep the blood circulation going’. So, not only giving an illusion of being healthy, they may actually be making you more so – whether you break a sweat or not.