Never wear navy, don’t do matching trousers and avoid feminine styles (yes, really!) The rules to wearing a waistcoat over 50 by fashion expert SHANE WATSON

I don’t know if you’ve noticed, but the waistcoat is really in, and not just for young women with bare arms.

In fact, waistcoats have become the pinnacle of easy Outfit Sharpeners. When a jacket is too warm or too formal, when a blouse is too slouchy and not neat enough, when you want to look a little more put together, you reach for a waistcoat. Best of all, a waistcoat turns one or two everyday pieces into a modern outfit. It couldn’t be easier!

There’s plenty to choose from this summer, including knit and silk styles, but the results of my not-so-scientific research show that linen cardigans in cream, ivory, light blue and grey reign supreme.

Actress Sophie Turner opts for the matching waistcoat and trouser look

Vests are on the rise – seen on fashionistas including actresses Zendaya (left) and Sophie Turner (right)

Women of all ages and shapes wear them with matching, tailored wide-leg trousers, as part of an extra summery (sleeveless) suit or with a jacket as part of a three-piece suit (not so much, as it can look a bit forced, especially in warm weather).

However, the most popular combination by far is a waistcoat plus a pair of ill-fitting, loose-fitting, tailored trousers. This combination has really taken off with the over-50s and all women who want something easy to wear on a warm day that is reasonably smart without being restrictive, yet flattering.

Flattering without being revealing is the key to a gilet’s appeal, by the way: a tailored gilet gives you definition without clinging to your body. It’s much the same principle as a knitted tank top in winter, only it’s more feminine because it’s structured and you can wear a gilet loosely and still get the benefits of a torso-defining look.

Meg Ryan shows how great a cardigan can look when paired with a long, flowing skirt

Meg Ryan shows how great a cardigan can look when paired with a long, flowing skirt

Still, there are times with a waistcoat when you wonder if they look a bit snooker pro, or Gareth Southgate at that, and the best way to avoid this is to mismatch your bottom half and avoid navy. Black always works. Cream is a definite summer hit, and a cream pinstripe looks great with any neutral trousers.

The White Company's cream pinstripe vest, made from linen/cotton blend

The White Company’s cream pinstripe vest, made from linen/cotton blend

The White Company has a beautiful linen/cotton blend pinstripe vest (on sale for £44.50, thewhitecompany.com) with faux horn buttons and a belt at the back. These classic details make a waistcoat look chic – you don’t want a girly waistcoat, just as you don’t want one that makes you look like an England manager.

The White Company also has a linen stretch cardigan if you want a slightly tighter fit (on sale, £55).

Otherwise the Marks and Spencer version, fully lined with welt pockets (£35, marksandspencer.com) has a slightly shallower V-neck, which works better in winter with a plain boyfriend shirt underneath. Get one in ecru or light blue now and one in black for fall and you won’t regret it.

Aside from sticking to a masculine shape, the details to look for in a waistcoat are a V-neck (round necks are harder to pull off); a V-shaped hem (straight is far less flattering); and a length that hits the hips – too short and you’ll have a gap between your waistcoat and trousers, too long and you’re into sleeveless jacket territory, and to me, they feel more formal. That said, I’d make an exception for M&S’s ivory pinstripe peak-lapel longline waistcoat (£49.50); ​​it has matching trousers, but I think it’ll look great with jeans and tanned arms come September, all being well. Either way, it’ll be an incentive to keep lifting those weights.

The ever stylish Trinny Woodall wears a three piece suit with gold high heels

The ever stylish Trinny Woodall wears a three piece suit with gold high heels

A knitted cardigan is a more casual, softer option that looks great with long, flowing skirts, one of which is from Massimo Dutti

A knitted cardigan is a more casual, softer option that looks great with long, flowing skirts. This one is from Massimo Dutti

You’ll want to wear your cardigan now, no matter the style, buttoned up, over a plain open-necked shirt, or nothing at all. Nothing underneath is of course the fashion-conscious way to go, and that’s how your daughter is wearing hers, fancy gold chains in the neckline optional.

If all that doesn’t sound appealing, a softer option that you can wear over a slim-fit top is the knitted cotton cardigan. This is more casual, but has the advantage of working well with longer flowing skirts if you’re not into trousers, while a tailored cardigan plus a midi skirt can make you look like the tambourine player in a 70s rock band.

Cos has a neat, three-button, ivory V-neck cotton-blend cardigan (£65, cos.com). Otherwise, Massimo Dutti has two smart knitted cardigans, one in a grey marl colour (£69.95, massimodutti.com), the other in a black and white mottled cotton blend (£89.95, massimodutti.com) in a boxy, edge-to-edge style with bows instead of buttons. In store they display them on mannequins with maxi skirts and softly flowing midis (both £89.95), so there’s something for everyone.

One more thing: a waistcoat is a very handy in-between-season item. Just saying.