Meryl Streep believes that she portrayed Margaret Thatcher in the "right way."

The 62-year-old actress plays the former British Prime Minister in upcoming biographical drama The Iron Lady.

Meryl has been criticised by former members of Margaret's political entourage for depicting the 86-year-old ageing octogenarian's dementia in a controversial manner.

Meryl portrayed the condition as honestly as she could.

"I felt that if we did it in the right way, it would be OK," Meryl told the BBC. "It's something that I don't think there should be a stigma about, it's life, it's the truth."

Margaret suffered from several small strokes in 2002. Meryl thoroughly explored that post-stroke headspace while portraying her character in the film.

"There is a feeling that the walls are just more permeable between the present and the past and one intrudes on the other," Meryl explained.

"We've all had that moment where you can't remember why you went upstairs and so it was extrapolating that feeling of disorientation, momentary as it is."

In 2008 Margaret's daughter Carol Thatcher published tome A Swim-On Part In The Goldfish Bowl: A Memoir.

The book illustrated Margaret's declining memory in detail.

"Carol caught a lot of flak for speaking about this in her book, but other people who have dementia in their family are grateful."

The Iron Lady will be released worldwide in January 2012.