There were rumours that Sienna Miller might skip the debut catwalk show of Twenty8Twelve, the collection that she co-designs with her sister, Savannah, in order to be at the Oscars. “As if,” said the actress, before the show. “I love being part of this, and I'm doing it to help my sister”.

“I hope that's not the only reason you're doing it, Si,” says her big (two and a bit years older and, at 5ft 10, five inches taller) sister. “Of course it isn't, Sav, you know that.”

The Miller sisters are so unguarded that interviewing them about this collection can feel like butting in on a family get-together. Bottom line: this is an appealing synthesis of their shared penchant for slouchy, hip clothes, with a nod to strong, Balmain-esque shoulders. There are cute, cropped trench jackets, rugged khaki parka-style coats, minidresses layered over denim leggings and luxurious knits. It's eminently shoppable and unpretentious. Which, with 70 stockists and a solid fan base, should make it perfect for now.

Some critics argue that clothes this easy don't need to be on the catwalk. But catwalks are a form of fashion oxygen. “If anything,” says Sienna, “the recession pushed us into doing this show. It was either blur into all those other labels or make a statement.”

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