The Iron Lady: Alexandra Roach on playing young Thatcher

Alexandra Roach was just three when Prime Minister Margaret Thatcher left office after 11 years in 1990.

Many people in her home town of Ammanford, an area of Carmarthenshire steeped in coal for generations, may have celebrated the departure of a leader at the centre of the divisive 1984-5 miners' strike.

But little did they know that the small girl in their midst would grow up to become an accomplished actress selected for the role of the young Margaret Thatcher in the film The Iron Lady, with double Oscar winner Meryl Streep taking over as the future PM enters parliament.

Roach's career path was a result of a chance decision to attend a drama class with her friend - and now fellow professional actress Sara Lloyd Gregory - on the day auditions were taking place for the Welsh-language soap Pobol Y Cwm.

The 11-year-old Roach got the part and spent the next seven years "practically living in the BBC in Llandaff [where the series is filmed]" playing the role of Elin Owen.

"That's where my passion was ignited, on the set of Pobol Y Cwm," she said.

"I loved it and I've had such a passion for TV and films. I can't do anything else."

After leaving Amman Valley School and spending a year at Gorseinon College, she studied for four years at the Royal Academy of Dramatic Arts in London.

A brief spell at the Almeida Theatre in London came next before that audition to step into the shoes of a young Margaret Hilda Roberts arrived.

After gaining the part, Roach says: "I had to live and breathe Margaret Thatcher for a few months.

"I totally engulfed myself in her life. I read her autobiography and a biography, The Grocer's Daughter."

Talk of Thatcher for those who lived through her premiership prompts images of an imperious, domineering premier, but all that had to be irrelevant for Roach, who takes the character from a teenager in Grantham, through university at Oxford and on to the married mother-of-two on the brink of entering parliament aged 33.

"There's only two interviews of her at 33," Roach explains. "From the famous Margaret Thatcher that we all know her voice was very different. Her voice was much higher, and it was interesting the changes it went through.

"Just trying to get the starting point in Grantham, and then it changed again when she went to Oxford - it's a step into the character."

Roach admits: "I was always really poor at accents in drama school but I've only played one Welsh girl since leaving drama school, so I don't know what's happened there. They've all been posh English girls."

For a girl from a mining town with miners in the family, was there a certain edge to playing such a polarising figure?

But Roach is keen to emphasise that she is playing Margaret Roberts, rather than the woman she became later.

"I heard her name growing up and I needed to go back and research, and not judge her," she says diplomatically.

"My grandfather was a miner and my father was a policeman and it was a tough time during the strike for the Roach family.

"I haven't really asked them about it. I'm only playing her up to 33. If I'd played her knowing she was going to be prime minister it would have lowered the stakes. She hadn't done anything to Wales at that point."

She knew this could be career-changing role the moment she heard about the audition.

"When I got the brief through for the audition and it said to play the younger version of Meryl Streep's Thatcher, I knew it was going to be a big film.

"To watch her and Jim Broadbent [who plays Denis Thatcher] work, it was overwhelming to be in the same room as her let alone share a character.

"It was my job to make the transition as smooth as possible. I'd go on set on my days off to watch her, for professional and personal reasons.

"It was easier for us [to share the role] because there's lots of facts to draw on and we know where we want to go with the character.

"She'd watch me do scenes and be really encouraging. She's such a wonderful woman that I wasn't nervous."

Roach's hope for her career path in some senses mirrors that of her co-star Streep, who has built a reputation on her ability to be absorbed into a role rather than star in a "Meryl Streep" vehicle.

She explains: "My ambition is to become one of those actresses that is like a chameleon that you don't recognise. Transformations don't scare me: it thrills me to become the polar opposite."

Aside from The Iron Lady, Roach has been kept busy in the short time since leaving drama school.

She has four films coming out shortly: the psychological thriller Trap for Cinderella; an adaptation of Michael Morpugo's World War I novel Private Peaceful; Anna Karenina with Keira Knightly and Jude Law and a BBC Wales film, Loserville.

She says of the latter: "Loserville was made by director Peter Watkin-Hughes to raise awareness of homelessness in Wales. My mother works for the children's commissioner for Wales so it's a subject close to my heart."

The Iron Lady has its UK premiere on 6 January.