SIENNA MILLER IS WEARING ONE ITEM ON REPEAT RIGHT NOW – AND IT’S IDEAL FOR UNCERTAIN SUMMER WEATHER

Last week, we were all test-driving our heatwave wardrobe, in the vain hope that the mercury would properly spike this summer. Now, it seems we're caught between dramatically changing temperatures, wind, some drizzle and sporadic bouts of sunshine. For anyone wondering how to style it out, Sienna Miller has the solution in the form of one item in particular: a pair of white trousers.

On the promo trail for her new film Horizon, Miller stuck to a tried-and-tested trend that's already seen several endorsements from the A-list: the all-white outfit. If that doesn't sound entirely practical, the actor's separates were eminently easy-to-wear - a white scoop-neck tank top and the aforementioned white trousers that looked smarter than cargo pants but more lo-fi than tailored pants (Reebok's Club C trainers added to the look's relaxed appeal).

Just days later, Miller made an appearance at Glastonbury, the scene of some of her most famous outfits past. For the occasion, she chose (quite punchily, considering the setting) the very same white trousers, this time paired with a checked Barbour jacket (now sold out) and short Barbour boots. If you were to ask me, which you sort of have, I'd wager a guess that Miller's new favourite trousers are this pair from Khaite, which, as the actor knows, have the perfect slouchy fit. That's clearly why they're selling so quickly.

If I were Miller, I'd feel a bit paralysed by choice of what to wear to Glasto these days, given the absolute mania inspired by her outfits from previous years (namely 2004). This convinces me that white trousers are a winner, then, as they have the ultimate seal of approval. The only rules? Wide leg styles look best, teamed with a tank top, tee or oversized jacket. Try a tucked-in shirt for smarter days and even wear over a swimsuit on holiday. It's what Miller would want.

Shop: Sienna Miller's All-White Outfit

Natalie Hammond is Grazia’s Senior Fashion News Editor. She loves winter, hates summer and can often be found writing about the weather (and what on earth to wear).