SIENNA MILLER - SIENNA MILLER CLUELESS OVER KEVIN SPACEY/BACON GAFFE

British actress Sienna Miller has said she is "baffled" at claims she mistook Kevin Spacey for Kevin Bacon at a recent A-list party.

The 25-year-old had reportedly been drinking champagne with the Oscar-winning Spacey for a couple of hours before dropping the clanger.

But Miller, who currently stars in Edie Sedgwick-biopic Factory Girl, says she has never even met the artistic director at London's Old Vic.

"Apparently I went up to him and said 'I can't believe I'm in a bar drinking with Kevin Bacon,' she said.

"And he said 'Spacey', and I went 'Isn't it?'"

The New York-born actress also recently revealed the secret behind her portrayal of Sedgwick – she remained in character at all times with co-star Guy Pearce.