Jenna-Louise Coleman at Margaret Street Gallery, London: ‘I was ready to leave Emmerdale when I did.’ Photograph: Katherine Rose for the Observer

Fittingly, for an actress who last year debuted as a time- and space-hopping adventurer in Doctor Who, Jenna-Louise Coleman is thinking about multiple universes. She recently saw Constellations in the West End, a play that took on the idea of there being infinite dimensions – other worlds in which everything that can happen does happen. Sitting in a London cafe, she reasons: if parallel worlds exist, there’s one in which I live in Hollywood and play an Australian in a sitcom, cracking terrible jokes about dingoes.

It almost happened: “Even though my Aussie accent is appalling,” says Coleman, 26, who got to the final auditions for the sitcom job, in Los Angeles in 2011, before being called back to England to appear in the ITV drama Titanic. That job opened up a seam of British work – a part in Stephen Poliakoff‘s drama Dancing on the Edge, a role in Doctor Who – that hasn’t let up since. The Poliakoff is an ensemble piece about 1930s jazz musicians. Meanwhile, she has made two meaty Doctor Who cameos to date, including a show-stealing appearance at Christmas, and will be the Doctor’s official companion in the next series. Coleman’s character is a woman called Oswin, who exists (uh-oh) across multiple dimensions.

It was all less complicated when she started out. At the age of 11, she went to an open audition in her home town of Blackpool and got a part in the musical Summer Holiday, starring Darren Day. “I played an Italian bridesmaid,” says Coleman, who remembers being paid £30 a week, plus a gift of Debenhams vouchers from Day at the end. At 19, she joined the cast of Emmerdale and for three years played a troublemaker called Jasmine. (Final scene: off to prison for committing murder with a chair leg.) “As a first job I’m grateful for it,” she says. “Though by the end I was quite restless. It was a brilliant experience. But I was ready to leave when I did.”

Post-Emmerdale, things looked bleak. She went six months without work (“There wasn’t any sniffiness in auditions about my soap background – I couldn’t get auditions”) and at one point she tried to get into Rada, unsuccessfully. “It was strange to turn around at 23 and think, I haven’t gone to university, I’ve missed out on that. And, shit, I don’t think I’m ever going to get another job.” She moved to LA to try her luck and ended up doing “two or three auditions a day”, which broke her duck. British jobs followed.

In Poliakoff’s drama, Coleman plays “a steely young girl with an extreme ambition in a man’s world. She wants to be a journalist.” It completes a circle back to her soap days, where at one point her bad-girl character became a tabloid reporter. If there is a parallel world in which Coleman stayed in LA, doing dingo jokes, there’s another in which she hung around on Emmerdale… She’s better off here, no doubt, in our present dimension.