Sienna's boutique binge leaves her the worse for wear

But Sienna Miller's generous intake of alcohol at the launch of her boutique left her looking anything but an advert for sartorial elegance.

The actress had to be helped out of the event's afterparty by friends after stunning partygoers by shouting obscenities and stumbling into a wall.

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Helping hands: Sienna's pals keep her in check as she stumbles out of the do

Party pals: Sienna looked rather queasy as she piled into a cab with actor Rhys Ifans

Despite being propped up and sporting what appeared to be blood stains on her oversized white shirt, the Factory Girl star, 25, wasn't ready to call it a night.

Instead, holding her hand over her mouth, a distinctly queasy-looking Sienna headed on to a house party with her drinking sidekick of recent weeks, dishevelled Notting Hill actor Rhys Ifans.

When that ended at 3.30am following neighbours' complaints about the loud music, the pair eventually lurched back to the actress's London flat, where Ifans had to help her fit her key in the lock.

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Mad hatter: Sienna Miller mingled with the rather eclectic crowd at the launch party

Friends worry Sienna's friendship with Ifans, 40, could be to blame for her erratic behaviour of late, as the pair have spent much of the past month lurching from bar to bar, as well as holidaying on the hedonistic party island of Ibiza.

Both deny they are dating, and Sienna insists Ifans has merely been sleeping on her couch since his houseboat flooded.

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Mess: blearly-eyed Rhys attempts to make a point

Sienna's appearance at the launch of her Twenty8Twelve boutique was supposed to be her attempt to be taken seriously as a fashion designer alongside her sister and co-partner Savannah.

But things quickly went downhill after Sienna eagerly downed Moet and Chandon champagne and Tom Collins cocktails.

A fellow guest at the event - attended by fashion photographer Mario Testino and designer Matthew Williamson - said: "The girls invited family and friends to join them in toasting their new venture - and boy, did they toast.

"It went on until the early hours, when they stumbled out of the afterparty at the Lonsdale bar nearby. They were more than a little worse for wear."

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Early morning glory: the pair stumbled home at 3.30am

Key influence: Rhys helps Sienna unlock to door to her London flat, where the actor has been 'sleeping on the couch'

According to one source, rivalry with Keira Knightley on the set of forthcoming film The Edge Of Love may have driven Sienna to seek solace in partying.

The friend said: "The reason she has been going off the rails and overindulging in the celebrity lifestyle is because she feels she is in Keira's shadow.

"They are good friends but she feels Keira's star is rising while she is not getting the same glory and not being offered the same high-profile parts.

"She has been going out on the town a lot as a result but it is beginning to take its toll, particularly as she feels she has to keep up with Rhys, who is a notorious party animal."

SIENNA AND RHYS: THE STORY SO FAR

Sienna and Rhys were first spotted together while on holiday in Ibiza earlier this month. Back in London, the pair caught up over a glass of wine. By Wednesday, Rhys, who is currently living with Sienna, was joining in on domestic life