Sienna steps out for premiere

The actress said she also tries her best to cut down on wasted energy by switching off her phone charger and plug sockets.

Sienna arrives in Leicester Square this evening

The British star was showing off her environmental credentials at the UK premiere of Factory Girl, in which she plays Andy Warhol's muse Edie Sedgwick.

The movie is a biopic of the 1960s It-girl and fixture on the New York party scene, who died of a drugs overdose in 1971 aged 28.

"I switch off my plug sockets at night and turn my phone charger off. I'm a great supporter of carbon-neutral," she said.

Miller - who turned up with her sister Savannah as her date - also admitted to loving her food.
Director George Hickenlooper joked that he had tried to stop Miller tucking into French fries and chocolate during filming but she simply told him to "bugger off".

Miller said: "He used to steal my bagels. He gave up because I love my food."

The actress said the premiere was "very exciting, it feels like a good party after lots of hard work."

She said she had enjoyed playing her first lead role: "You try to lose yourself in the moment."

And she praised co-star Guy Pearce, who plays iconic pop artist Andy Warhol, saying: "Guy Pearce is a great actor, a great friend and totally embodied Andy."

Miller wore a vintage cream and black Balenciaga mini dress, black tights and black Sergio Rossi shoes as she walked down the pink carpet outside London's Vue Leicester Square cinema.

Her sister wore a grey dress from 2812, their clothing label due in shops from July.

Hickenlooper said he was thrilled that hundreds of people turned out to the premiere.

"I'm so flattered all these fans are here," he said. "I like the British, it's a more literary climate so maybe they will appreciate the film more."

Among the famous faces who turned out to support Miller was actor Rhys Ifans, who said he had seen the film and added: "She was amazing. It's a marvellous transformation and she's in the knack (nude) so you can't go wrong."

The film attracted controversy with its depiction of a doomed affair between Sedgwick and a musician, played by Hayden Christensen, and Miller has dismissed rumours that the sex scenes between her and Christensen were genuine.

Singer Bob Dylan is reportedly unhappy about the musician character, believing it is based on him and that the film falsely blames him for Sedgwick's death.