Here’s something you don’t hear every day. This summer’s most useful accessory, the item that will make the everyday instantly stylish, is one you already own.

It’s in a drawer, maybe with a lavender bag. It’s plain, it’s wool, it is (drum roll) the humble crew-neck, long-sleeved sweater.

For now you’re not putting your arms in the sleeves. Or your head through the neck hole (it’s summer after all and this sweater has been repurposed until further notice).

We’re calling it the sling-around sweater (SAS for short) and it’s the fastest route to anti-ageing your wardrobe, without spending a dime.

This is hardly a new idea. We know about slinging a sweater around our shoulders and the fashion front row have been at it for well over a year now.

But as of this summer the look has crossed over, from fancy styling flourish you see at the shows to mainstream fashion hack.

What’s more, it’s both a cool styling trick and a practical assist that everyone can join in with. We wouldn’t necessarily bother to wear our collars flicked up, or a shirt half in, half out – French tuck style – but the SAS feels natural, looks natural and, apart from being on the fashion bullseye, it really does make clothes more wearable.

If you’re in the Fifty Plus category it could be the difference between going sleeveless or not.

Here’s everything you need to know if you want to get the most out of the summer SAS...

Daisy Edgar-Jones wore a beige sling-around sweater (SAS) round her neck for the Cannes Film Festival

Kendall Jenner also has a SAS - though she likes to wear it around her waist

  1. Your SAS needs to be soft and light to medium weight. A chunky cable knit or hairy wool sweater will look too heavy in warmer weather and won’t sling and drape elegantly.

You’re also better with wool than cotton (more elegant) and a straight sweater is better than a cardigan: less messy.

  1. With bare arms and a low neckline, you can wear your SAS simply draped down your back with the arms looped once across your chest. This gives you a little bit of extra coverage and adds another texture and colour (see actress Daisy Edgar-Jones arriving in Nice for the Cannes Film Festival in her white sleeveless sundress and beige SAS). She looked roughly 80 per cent more elegant, just like that.

  2. The SAS can act like a shawl without looking dowdy – as a shawl most definitely would on us. It softens the neckline of a smart tailored dress. Provides a hint of structure in the absence of a jacket, worn across the shoulders of a shirt.

And if you have the arms to wear a vest top, an SAS is useful for those occasions when you want a little bit more coverage.

  1. Choose any colour, so long as it’s plain and not pretty. An SAS can work as a punchy disruptor – a flare of unexpected colour in an otherwise minimal outfit; it can add a subtle extra tonal layer; or it can look chic doubled up with a T-shirt the same colour.

See Daisy Edgar-Jones, again during Cannes week, who looked super-chic wearing a grey wool T-shirt paired with a matching SAS, loose-fit white jeans and black pumps. Cream on white works well. Red with black is a current favourite fashion go-to. Grey is a grounding colour that will work into the winter with tweeds and checks.

  1. Consider slinging a sweater around your hips or waist. You might assume this is only going to add bulk where you least need it but, providing you stick with light, soft sweaters and you’re averagely tall, it’s a genuinely forgiving alternative to a belt.

A little black sweater tied loosely around the hips of a pair of straight white jeans (a favourite Kendall Jenner look) adds smartness not inches. Wear it arms tied in front and draped over your bottom and it’s a cover-up too, if that’s what you fancy.

Otherwise, a little red sweater tied to one side around the waist of an LBD, or a midnight blue one slung around the waist of a jumpsuit to break up the silhouette. Perfect.

  1. Bear in mind that this is not a one-season-only look. Back in the spring, the fashion-forward were wearing sweaters draped over the lapels of their trench coats.

When the weather cools, or on breezy summer nights, the modern alternative to a pashmina or shawl (top of the instant-ager list) is an SAS worn over a buttoned-up khaki jacket or knotted at the throat of a blazer.

If there’s an easier way to anti-age your summer look, I can’t think of it.