She 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," the star said.

Sienna - 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".

Sienna 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."

Sienna’s foot in mouth syndrome - Mar 6 2007
Sienna Miller has apparently explained her tendency to explode in angry rant, saying she suffers from "mild Tourette’s syndrome".

The 25-year-old says she can’t stop "putting a foot in it", saying sometimes outlandish things without meaning to, according to The Sun.

The Factory Girl star told the paper: "These things just come out of my mouth. I’ll say the most inappropriate things, guaranteed... but I don’t deliberately hurt anybody."

Sienna is apparently worried that she has the neurological disorder which Big Brother winner Pete Bennett famously suffers from.

In the past, she had made a few verbal faux pas including calling US city Pittsburgh ’S***sburgh’, while filming there. She later apologised.

But it looks like the actress’ new love, 21-year-old millionaire’s son Jamie Burke, doesn’t have a problem with her habit.

The pair were recently spotted getting cosy together on a beach in Mexico, while Sienna sunbathed topless.

Sienna smooches with new man? - Feb 23 2007
It seems the mystery of Sienna Miller’s love life has finally been unravelled - she’s been spotted looking cosy with millionaire’s son Jamie Burke.

The twosome were snapped looking intimate on a beach in Mexico, with Sienna sunbathing topless and gazing into former public schoolboy Jamie’s eyes.

Onlookers told the Daily Mirror the duo were all over each other, with 25-year-old Sienna giving Jamie a sizzling smooch in full view of other holidaymakers.

"They were like a couple of lovestruck teenagers," a source told the paper.

It seems Jamie, 21, is no stranger to dating famous women - the long-haired hunk has been linked to supermodel Kate Moss, rocker Courtney Love and US starlet Lindsay Lohan, according to the Mirror.

And Sienna’s no slouch in the famous exes department, having romanced Hollywood heartthrob Jude Law and been linked to Daniel Craig, her Factory Girl co-star Jack Huston and Isaac Ferry, son of singer Bryan Ferry.

Sienna to team up with 007? - Feb 14 2007
Sienna Miller is reportedly set to star alongside her ex Daniel Craig in the next James Bond flick.

The 25-year-old blonde has previously starred with the hunky actor in gangster film Layer Cake - where the couple had a brief affair.