SIENNA MILLER “adds the sex” to sister Savannah’s fashion designs, the pair revealed in the run-up to London Fashion Week, which starts next month.

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“Sienna’s edgy and out there; I’m soft and romantic,” said Savannah, a Central Saint Martins fashion graduate. “I have an idea for a design and she adds the sex and flips it on its head. It’s fun and it works.”

“Working with her is always great as she comes up with crazy ideas that I perhaps wouldn’t otherwise consider.”

The siblings have two shops in London, one in Westbourne Grove, the other in the new Westfield mega-mall.

February’s London Fashion Week has been sliced down to five days to fit in with date changes to New York’s more favoured show, but the presence of star quality like Sienna is likely to keep the event in the limelight.

“We are so excited,” said the Millers. ” We felt ready to be taken to the next level.”