'Dreams of a Life': The ghost of Christmas not so long past

Dream role: Zawe Ashton in the forthcoming drama 'Dreams of a Life'

While many actors relish playing real-life characters, the challenge facing Zawe Ashton in the acclaimed new docudrama Dreams of a Life was very different from portraying, say, Maggie Thatcher or Marilyn Monroe. Ashton plays Joyce Vincent, the woman who died mysteriously in her North London bedsit in 2003 and whose body, surrounded by unopened Christmas presents and with her TV still on, was only found three years later.

"Roles like this don't come along often," says the 27-year-old half-British, half-Ugandan actress . "It just brought every single challenge into play that I could ever imagine. That's what interests me when I approach any role – who do you really know?"

Personally affected by Vincent's tragic end ("I emailed my agent when I got the script and said, 'this is me'"), Ashton immersed herself in a wealth of accrued data, pictures and music, discovering a deeper connection than she had ever envisaged.

I had these huge, blown-up photographs [of Vincent] with me all the time and I took one of Joyce and Kyle, the young boy who used to brush her hair, round to show my mum," relates Ashton, "and she said, 'oh yes, you and your brother'. I was like, 'whoa, no mum...' Then she looked closely and was taken aback by the similarity."

Ashton's mother wasn't alone; Vincent's friends approached the actress after the first screening, marvelling that, "that was our Joyce", onscreen. "Seeing these people I'd been living with in my head was really bizarre," remembers Ashton, almost like I knew them. I felt very protective of them."

Ashton's star continues to rise as both actress, in the Channel 4 student comedy Fresh Meat and the BBC crime thriller Case Histories, and writer (she's writer in residence for women's rehabilitation theatre company Clean Break and is developing a script with the actor Idris Elba). On Christmas Eve she will appear in the 90-minute comedy Lapland opposite Sue Johnston and Stephen Graham.

In the meantime, Dreams of a Life is "a game changer", she says, but one that clearly dovetails with her own artistic ambitions. "Something in me just has to give a voice to the underdog or the voiceless," she says. "Dreams of a Life is actually a celebration of Joyce's life. We wanted to give her her voice and life back again."

'Dreams of a Life' opens in cinemas on 16 December; 'Lapland' airs on Christmas Eve at 10pm on BBC1