She is known as one of world's most glamorous actresses.
Baroness Thatcher's father ran a grocer's
But Sienna Miller's latest film role may be a million miles - or at least about 6,000 - from the glitz and excitement of Hollywood.
The 25-year-old is reportedly being lined up to play a young Baroness Thatcher, who grew up above a shop in Grantham, Lincolnshire.
Ms Miller's spokeswoman refused to deny reports she was considering the role, adding: "Nothing has been confirmed."
Hollywood director Oliver Stone, whose previous films include Wall Street, Platoon and Natural Born Killers, is believed to have wanted to make a film about Baroness Thatcher - born Margaret Roberts - for several years.
Actress Meryl Streep has previously been linked with playing her.
Sienna Miller is used to more glamorous roles
Baroness Thatcher, who was prime minister from 1979 to 1990, went from Grantham to Oxford University, where she became president of the Conservative Association.
She became an MP at the age of 34, having been part of the team of scientists which developed soft frozen ice cream.
Ms Miller's previous film roles have included a Cockney gangster's glamorous girlfriend in Layer Cake and the heiress and Andy Warhol "superstar" Edie Sedgewick.
The Thatcher role could include the former Conservative prime minister's upbringing above a grocer's shop in Grantham, Lincolnshire, and her later training as a chemist.
Separately, it was announced earlier this year that the BBC and Pathé were planning a film about the decisions faced by Baroness Thatcher in the run-up to the 1982 Falklands War.