PASADENA, Calif. — Matthew Macfadyen is perfectly presentable in jeans and a crewneck sweater that coordinate nicely with the blue of his eyes.

But the look is far from the elegant attire he wore as Mr. Darcy opposite Keira Knightley’s Elizabeth in the 2005 film “Pride & Prejudice.” And his posture is just as casual, which he acknowledges might offend the aristocratic character’s diehard fans.

“You’re slouching! What are you doing? Stand up straight, man!” Macfadyen says, teasing himself.

He looks back fondly on what he calls the “iconic” role drawn from Jane Austen’s novel. But the British actor who’s also known to audiences for his part as an intelligence officer in the spy series “MI-5” welcomes the chance to switch gears.

“I, as most actors, want to mix it up and do different things. Otherwise, it gets boring and tiresome, not only for yourself but for everyone else seeing you do the same kind of thing,” he said. “The joy of being an actor is to play different parts, do something different.”

Macfadyen’s latest chance for diversity comes in “Ripper Street,” an 1880s police drama set on the gritty and untamed streets of London’s East End around the period that serial killer Jack the Ripper terrorized the area.

The series, starring Macfadyen as Detective Inspector Edmund Reid, recently debuted on BBC America. BBC America is home to another rough-and-tumble, 18th-century police drama, “Copper,” set in 1860s New York.

The mysterious and brutal Jack the Ripper has been recycled throughout pop culture in films including 1979’s “Time After Time” and 2001’s “From Hell” with Johnny Depp. But series creator Richard Warlow said the killer is a backdrop and invisible character for “Ripper Street.”

“What we wanted to do really was to tell stories about the streets down which he walked and committed his crimes in the wake of those terrible murders,” Warlow said, “and how it affected the community and, most importantly, the police that tried and failed to catch him.”

Each episode will include what he called a “stand-alone crime” as well as pull at the thread of Reid’s life, including those surrounding him at work and at home.

Macfadyen said he was reluctant to take on another series after two-plus seasons on “MI-5” because of TV’s demanding production schedules. Then the “Ripper Street” pilot script came his way last year.

“I thought the Jack the Ripper thing had been done before ... but I loved it. The thing that was most attractive was the language and the way he (Warlow) constructs the sentences. ... They feel very muscular without feeling sort of wanky and silly.”

There is an antiquated eloquence to the dialogue that contrasts with the drama’s mean streets and violent sexuality of the first case tackled by Reid and his cohorts, police Sgt. Bennet Drake (Jerome Flynn, “Game of Thrones”) and American forensics whiz Capt. Homer Jackson (Adam Rothenberg, “The Ex List”).