Hugh Bonneville was more than happy to hang up his “monkey suit,” the tuxedos, uniforms and evening clothes he’s oft encased in on “Downton Abbey.” “Oh my heavens, yes!” But it took a movie, with him co-starring with a cuddly bear, to manage it.

“As much as I love ‘Downton Abbey,'” the actor who embodies the inimitable Lord Grantham says, “it’s nice to put on a sweater. Occasionally.”

Bonneville is Mr. Brown, the stuffed-shirt “risk analyst” father who resists the idea of his family adopting a refugee bear in the charming new film, “Paddington,” based on the much-loved children’s books. The role, Bonneville confesses, isn’t a huge stretch.

“I think Robert Crawley (Lord Grantham) is a distant cousin of Mr. Brown,” Bonneville says. “I’m not sure Lord Grantham would be caught dead sneaking around the ledges of the Natural History Museum (as Mr. Brown does, in one scene in “Paddington”). But there’s this patriarchal archetype that they both fit into, isn’t there? This buttoned-up father who, like Captain Von Trapp (“The Sound of Music”) or Mr. Banks “(Mary Poppins”), finally learns to ‘fly his kite,’ so to speak. It’s common in so much family literature and entertainment. Even in ‘Peter Pan,’ Mr. Darling is a bit clueless.”

Bonneville, 51, had been plugging along in supporting roles on film (“Notting Hill,” “Iris”) and British TV (“Lost in Austen”) before “Downton” took Britain by storm, and then the world. Lord Grantham, the earl and patriarch who presides over a baronial estate from World War I onward, came into his life and sort of took it over.

“I remember going on ‘The View,’ and Barbara Walters being so VERY disappointed that I was wearing jeans,” Bonneville says. “She tweaked my knee and said that wasn’t allowed, not for me, any more.”

But “Paddington” he just had to do.

“The name ‘Paddington,’ for generations around the world, particularly those of us who grew up in the U.K., is much more than a train station,” he says. “It takes you back to your earliest memories of books, back to your childhood. Those were the first books I was able to read to myself, so he’s held a special place in my heart.”

A veteran of the “Harry Potter” films would produce, and co-stars from Sally Hawkins to Oscar winner Jim Broadbent would be in the cast. But Bonneville had his concerns.

“I worried that Paddington would be bastardized in some way, or characters would be skewed beyond recognition. Within the first page, I was laughing. First sight gag, in the script, this ‘modest timepiece’ being carried through the jungle – and it’s a grandfather clock. When you’re laughing on page one, weeping on page eight and laughing again on page 10, that’s a script you want to do.”

“Paddington” arrives in theaters as, by far, the most critically-acclaimed film of the new year. Sandra Hall of Australia’s Sydney Morning Herald singled out Bonneville’s contribution to that, praising the way he “employs some of the stuffiness of his ‘Downton Abbey’ gig and adds a well-judged dose of self-mockery.”

Bonneville, in a bit of Grantham-esque jingoism, loves the Britain that the film depicts, “a magical version of London, the London we’d all love to think is real.” Bonneville laughs at the “old fashioned London” Paddington has been taught to expect, with it’s “politeness, always tipping your hat, and the ‘107 ways of describing rain.’ It’s a city with its ugly, dirty side, too.”

Still, it’s that bear-out-of-his element story that first grabbed kids when Michael Bond’s “Paddington Bear” books launched in 1958. Paddington’s experience is like a child’s first day at a new school, or a tourist’s first day in a foreign land.

“I always think that your first day in a foreign country, you’re either going to get fleeced or conned,” Bonneville laughs. ” You won’t understand the currency and make some huge mistake. Or the taxi driver in London or Chicago or Paris is going to take you the long way round. By the end of Day One, you’re a little less wet behind the ears. That, to me, is ‘Paddington.'”