Sienna Miller’s style evolution over the last two decades has taken her from the queen of boho (Miller says she spent her life “pottering around markets and layering a million different things”) to an understated style icon whose undone, effortless looks on and off the red carpet have us all captivated.

Her off-duty style has become increasingly relaxed in recent years, and when the actor recently told Stylist that jeans, a nice jumper and accessories was her go-to formula for day-to-day dressing it was no surprise. The actor has always been a fan of the effortless formula and often throws a T-shirt or vest and a blazer into the mix too.

Speaking at the launch of her collection for M&S, Miller explained her love for low-key, British style. “There’s no one that does undone, relaxed chic like the Brits; it’s something to do with the irreverence of being English and the humour, there’s just something about British style.”

It’s this undone, relaxed day-to-day style that’s key to Miller’s off-duty looks. It’s considered, not accidental, but it’s born from an innate understanding of what looks good on her and a knowledge of what’s new and exciting in fashion. It’s something unique to Miller but also a formula that fashion editors like myself employ regularly. It requires asking yourself what you feel good in (bearing practicality in mind), and for me that’s wide-leg jeans, flat shoes and a roomy T-shirt, shirt or knit. Secondly, you want to examine the details of those pieces and take time to consider what works well with what.

Sienna Miller’s go-to dressing formula is a fast-track to effortless style