Sienna and Savannah: sisters of style

When Savannah Miller was 10, she used to dress her younger sister Sienna up for fun. "I'd make her wear purple chiffon harem pants with an M&S bra I'd embroidered myself, and turn her into a little belly dancer. Looking back, I can see that we've been working together on clothes in some capacity for as long as I can remember."

Twenty years later, the Millers' fashion label, Twenty8Twelve is a little more sophisticated than those early efforts, and worn by everyone from Pixie Geldof to Thandie Newton. Slickly tailored with elements of rock-chick cool, the brand is on its sixth season, having launched to immediate success in autumn-winter 2007.

"When Sienna and I first started, it was about designing clothes that we would want to wear," the 31-year-old explains. "Now, I feel the clothes are more about what our clients would want to buy, which is not always the same thing. I've learned to understand the customer, while remaining true to who we are."

Sienna, 28, may feature throughout the Twenty8Twelve lookbooks, but there was no question of her walking down the runway when they presented the collection at London Fashion Week on Sunday. "We've always tried to avoid making the label too narcissistic, otherwise it all gets a bit cheesy," she winces.

Despite spending much of the past year on opposite sides of the world, the autumn-winter 2011 collection was a dual effort, like every other, Savannah says. "I had to fly back and forth a lot, but, thankfully, she's now back in the UK. Sienna does a lot of shopping in vintage shops, so we'll pick out details we like and Sienna will carry that design through with the rest of us. Once it's done, we try everything out on her."

Three ranges

In keeping with Twenty8Twelve's "soft with a hard edge" aesthetic, next season's looks are an eclectic mix.

"There are three different ranges. The first was inspired by the American political activist, Johanna Lawrenson — so pretty dresses with your boyfriend's army jacket worn over the top — and the second is glam-rock meets Adam and the Ants, with pop-like colours and plenty of velvets and silks. Then the third is Eighties and sporty."

Savannah has worked with Alexander McQueen, Anya Hindmarch and Matthew Williamson. Her former boss and mentor's death recently has left her numb, she says. "He was really trying to get himself together, but I think that after his mum died, he just got stuck.

"I worked closely with Lee for years, and I became obsessed with him. That man had a mind unlike any person I have ever met — he was like 10 people in one person's body."

The fashion world, Miller admits, has the capacity to "push you to the edge". "It's bloody hard work, especially if, like me, you have stupidly high standards, but there are areas in which I refuse to compromise. If I want to use a beautiful silk-velvet, and it works out too expensive, I'll just make a minidress out of it."

Nothing in the collection, the sisters have vowed, will ever be over £500 (Dh2,839). "And if it is £500, then it'll be something incredible, like the little shearling waistcoat we've designed for the autumn-winter collection."

Now with three shops in the UK, the Miller sisters seem to be on to something. "My dream would be to have stores in New York and Paris," smiles Savannah, "and incorporate shoes, swimwear and underwear into what we do — sell a total look."

There is no greater job satisfaction, she says, than seeing a woman in the street wearing her designs.

"I will never forget wondering through Covent Garden one wintry day and seeing this girl wearing one of our poplin summer dresses with black tights and boots, and a chunky black cardigan. She looked wonderful in a way I would never have expected; I love that people can take something of ours and make it their own."