Nick Briggs / Carnival Film for Masterpiece via Tribune News ServiceAllen Leech, left, plays Tom Branson to Michelle Dockery’s Lady Mary Crawley on PBS’ popular series, “Downton Abbey,” which premieres its fifth season Sunday.

BEVERLY HILLS — Actress Michelle Dockery finds herself intimidated by every new role. “I feel like I know I can do it, and I see myself doing it, but there is this fear of being bad or failing. I think all actors have it. It’s what makes us nervous and sometimes a bit neurotic,” she says in a meeting room at a hotel.

“You just want to be truthful and real. And I never think I’m going to be brilliant in anything. It’s not self-doubt as such, it’s just a very natural thing in an actor; a natural feeling of not being believable.”

When she first read the role of the aloof Lady Mary in “Downton Abbey,” Dockery was scared. “I read that part and thought, ‘I want this part so much!’ It’s rare, actually, that a part comes along and you really believe that this is the part for you. I have that thing where I’m like, ‘Oh, I’m sure they’ll probably go with someone younger, or they’ll go for someone older. I like the part but. . .’

“Then every now and then, something comes up and you think, ‘This is MINE. I know this character. I want to play this character!’ That’s how I felt about Mary. But at the same time she’s a character — I’m from a com-PLETE-ly different background. The accent was something I had to really work on. It was a challenge and it still is.”

How she rose to the challenge has become part of television history as “Downton Abbey” became one of the most popular dramas ever to grace the tube. And Dockery’s pale and contained Lady Mary crystallized an unparalleled cast performance and earned her three Emmy nominations. The hotly awaited show launches its fifth season Sunday on PBS’ “Masterpiece.”

When Dockery auditioned for the part, the producer of “Downton” had seen her play the guttersnipe Eliza Doolittle in “Pygmalion,” a character eons away from the upper-crusty Lady Mary Crawley.

“I thought of her as a young Kristen Scott Thomas, like the role she played in ‘Gosford Park,’” says Dockery, who’s dressed in a sleeveless white chiffon dress and black ballerinas.

“She’s the young, haughty aristocrat. So I got the character straightaway. I walked away (from the audition) thinking they’ll probably give it to a really well-known actress. At the time there were a lot of actresses who were doing loads of period drama in films. I just thought, ‘Oh, someone’s definitely going to want to do this role.’

She knew by the end of the day that she had been cast. “But I never knew it would change my life the way it did,” she nods.

Shy by nature, Dockery wasn’t prepared for the media blitz that followed. “The fame that comes sometimes can be overwhelming,” she says, sighing and leaning back in her chair. “Even the first year of ‘Downton.’

“It aired, the following Sunday the three (Crawley) sisters were on the cover of three newspapers in my local news agents. I couldn’t believe it. Of course, it’s exciting and it’s thrilling but then suddenly you’re not anonymous anymore. That was a big adjustment for me because I’m very shy among big groups of people. I can be better in just a one-to-one — that was an adjustment, really, for me.”

She says there’s no way to prepare for an eruption like that. “But it’s having good people around you who know who you are in spite of all that, they know who you were before. It’s the people who knew you before that happened, they’re the ones to cling to,” she says.

For her, that means her family and her sweetheart, John Dineen, who works in financial publicity. They were introduced a year ago last May by actor Allen Leech, who plays Tom Branson on the show. And while she’s reluctant to discuss him, she says meeting Dineen changed her life.

The woman who toiled as a waitress in a fish-and-chip cafe, served as a bar maid, as a recruitment temp for the Times, and later fumbled orders in an Italian restaurant, recalls that drama school was expensive, and she had to do what she could to earn a living. “There were times I couldn’t quite make my rent, but I’d always find a way of earning money here and there,” she says.

“My family are very hard workers. My dad, he was up and out of the house at 7 o’clock during the day. He did all sorts of jobs when I was growing up, a lot of driving jobs. . . He did a lot of delivery work. I remember when I was off sick from school, going off with my dad in his van. Then he got his degree in his 50s as an environmental chemist, so he’s a surveyor now and he’s been doing that since I was 14 or 15. I actually find it very easy to get out of bed in the morning. I think that’s from my dad.”