They usually form the underpinning of a look. But now bras are going from invisible to visible. Out are seamless T-shirt bras. In their place? Lace, sheer and mesh versions.

M&S, the home of sensible lingerie, is championing a sexier aesthetic for spring. The retailer holds 38.2% of the bra market in the UK and in 2023 sold more than 20m of them, with customers under 30 making up nearly a third of sales.

At a preview of M&S’s new collection on Wednesday, a £10 lace bra with bow detailing was spotlighted as a key piece.

Soozie Jenkinson, the head of lingerie design, says: “For years it was all about a T-shirt bra but now it’s about the return of lace.”

While the bras are not specifically designed to be worn exposed, their popularity marks a sharp shift from T-shirt bras that are designed to disappear beneath clothing.

At the British lingerie brand Bluebella, bestsellers include a £44 sheer black bra with scalloped edging and a £39 mesh bra with floral embroidery around the cups. Even its basics line features mesh and lace pattern bras in fiery shades of orange and electric blues.

Emily Bendell, the founder and CEO of the brand, says demand is coming from customers shifting their perception of what practical underwear is. “We believe the bra isn’t just a functional garment, but a fashion piece that should reflect the wearer’s style,” she says. “More and more women are rightly seeing their bra as a layering piece that they may choose to show part of – as part of their outfit.”

While previously the obvious shadow of a black bra under a white cotton shirt or irregular texture caused by a lace bra under a silky top would have been considered a wardrobe malfunction, now anything goes. The trend taps into a wider exposure movement.

In recent months, we have seen the revival of the noughties whale tail (where a thong is purposefully displayed), boxers deliberately styled to sit above a waistband and pants as actual pants. Now divulgence is shifting higher up the torso.

It is a trend that has stemmed from the red carpet. The actors Sydney Sweeney, Scarlett Johansson and Natalie Portman have worn dresses with bras peeking out from the neckline. At Trump’s inauguration in January, Lauren Sanchez intentionally exposed her white lace bra with a white Alexander McQueen blazer.

It is also a popular look on the catwalk. At Paris fashion week, Dior placed lacy bras under even lacier dresses while several of Sarah Burton’s looks for her Givenchy debut included bras that were in-built into mesh dresses.

Meanwhile at Miu Miu, the brand that previously kickstarted the latest iterations of VPL, this time round Miuccia Prada showed dresses and tops that appeared to be falling off the model’s body, exposing their bras. Other models wore conical shaped bullet bras underneath light knits and silky tops.

For those who are unsure, the American brand Vaquera offers the best of both. Its crew neck T-shirt features a trompe l’œil of a black lace bra. And yes, it can be worn with a T-shirt bra.