Meryl Streep had been looking to take on a project like 'The Iron Lady' for "a long time".

The Oscar-winning actress - who portrays infamous British political leader Margaret Thatcher in the upcoming movie - was hoping to take on a role that spanned a number of years, as she felt it would be an "extraordinary challenge".

Phyllida Lloyd, director of 'The Iron Lady', explained: "Her first reaction was that for a long time she'd been looking for a project that considered the end of a life, and she thought this would be the project.

"In other words, her access point to this was not... of course, it was the opportunity to play somebody over the course of forty years, which was an extraordinary challenge for any actor, but it was very much the old lady in the present day that gave her the igniting Spark for the project.

"She didn't see it as a biopic. She saw it as a story about something else, a bigger story, about the cost of a big public life and the cost to self, family, colleagues, etc."

The director - who also worked alongside Meryl in 'Mamma Mia!' in 2008 - explained while she, writer Abi Morgan and producer Damian Jones had considered other actresses for the leading role, ultimately they felt only someone of the star's "magnitude" could do the part Justice.

Phyllida added in an interview with "We did discuss other possibilities, and her, and then we quickly all agreed that to play somebody of the magnitude of Thatcher, you needed somebody of the size of Meryl."