Toby Jones stands up to illustrate a point. Delicately as a sapper stepping through a minefield, he moves towards an imaginary elevator. We are discussing his interpretations of real people such as Truman Capote, Alfred Hitchcock and Karl Rove. Characteristically, he needs to move to express himself.

“If we knew how Karl Rove picked up a phone or pressed a lift button, there wouldn’t be any need to make a movie,” he says.

“What can I say about this guy when I am on my own in a room? There are those great bits in movies when you just get to interact with yourself in a space. You eat an egg. You touch a lift button. People think they know these people, but they don’t.”

What a singular actor. Jones’s voice is now familiar: a classless warble with many angles in the vowels. We know him as a short man whose receding hair always seems to be striving for freedom in rebellious clumps.

But it’s the way he moves that really sets him apart. We should not be surprised to learn that Jones – son of the great character actor Freddie Jones – trained at the famously exhausting L’École Internationale de Théâtre Jacques Lecoq.

They take their clowning seriously there.

“They talked a lot about trying to remain vertical when everybody is trying to send you to the ground,” he says. “There is this constant attempt to maintain dignity. Staying upright is all.”

There’s a lot of that – both literally and figuratively – in Toby Jones’s current role. Few of the once-real, fleshy human beings he has played have quite the iconic resonance of the entirely fictional Captain George Mainwaring.

When it was announced that a film was to be made of Dad's Army, more than a few fans placed heads in hands. Early intelligence about casting then cheered the spirits. Michael Gambon as the incontinent Private Godfrey? Tom Courtenay as the ancient Lance Corporal Jones. Toby Jones stepping into Arthur Lowe's brown boots as Mainwaring? This might work after all.

"I thought a lot about it after being cast," he muses. "Am I playing Arthur Lowe being Captain Mainwaring being me? I don't really have an answer. But I did find myself watching an episode of Dad's Army from a different era every night. I wasn't trying to avoid him. But the rhythm of film is so hectic it means those worries get cast into the background. I do like it when people say: it's not Arthur Lowe, but there's a hint of him."

Set among the volunteers in a Home Guard platoon during the second World War, Dad's Army, which ran from 1968 to 1977, sparked on the contrasting styles of the era's greatest character actors.

There was, of course, a great deal about class in there. Sergeant Wilson, played by John Le Mesurier in the series and Bill Nighy in the film, is a great deal more posh than his superior officer.

I begin to detail incidents from key episodes. Jones smiles indulgently.

“I bow to your deep knowledge of all the episodes,” he laughs. “However asymmetrical they are about class, the platoon gets the job done. I think that’s the point. Sometimes Wilson and Mainwaring are genial. Sometimes they’re really at one another. They’re like masks. It’s a traditional comic troupe where every comic type is covered. It’s Commedia dell’arte.”

It comes as a mild surprise to learn that Freddie Jones never appeared in Dad's Army. A madly charismatic Northern hulk, Francis has been adding colour to British film and TV for 50 years. He was the cruel ringmaster in The Elephant Man. More recently, he has been a regular in Emmerdale. Did he seem like a famous man when Jones was young?

"He did seem famous, yes," he says. "He was in a few iconic children's series at the time: Children of the Stones and Ghosts of Motley Hall. He was famous among the other kids. Then they'd see him in Frankenstein Must be Destroyed.

“When I was 14, he was working with David Lynch and he therefore became really cool. So, I have always been struck by the affection that he’s held in by the public. So many actors have a story I may or may not want to hear about a late night with him. Ha ha.”

He remembers Freddie being largely supportive of his son’s decision to take to the stage. As Toby explains things, the business had changed so much the older Jones barely recognised it. Gone were the days when you could “stroll into the Granada TV canteen and emerge three months later having done two series”.

Jacques Lecoq’s college in Paris is famously rigorous. Students are driven to tears in their efforts to satisfy a perfectionist clown master. Even unemployment is frowned upon.

“It would be great to romanticise my past,” Jones says. “But it was standard procedure where I trained that you leave Paris and then you join a theatre company you have made. You have been taught to make your own work. You belong to a tradition that goes back before there were directors or producers. There were just actors travelling alone.”

Sure enough, a man with a defiantly distinctive face, Jones seems to have worked steadily throughout the 1990s. When did he gain his current status as ornament to the nation?

His Truman Capote in Infamous was on a par with Philip Seymour Hoffman's in the inconveniently contemporaneous Capote. He's super in Tinker Tailor Soldier Spy and Berberian Sound Studio. At any rate, somewhere in the past 10 years, he became an offbeat star.

“It’s a sensitive area,” he says. “On the one hand, my job depends on my being able to wander round and get on the Tube. Be a citizen. See how people carry their shopping, how they’re using their phones. That’s the real source material. I feel I can still do that.

“Yes, people come up occasionally, but they are always positive. I don’t question how well known I am. I feel somewhere in there I might encounter a curse. I might put a hex on things if I contemplate it.”

Toby Jones seems to have kept his feet on the ground. He and his wife, Karen Jones, live with their two children in a corner of busy, multicultural Brixton. Would it make sense to suggest that Karen, as a criminal barrister, uses some of the same professional muscles as her husband?

“We are both involved in the business of biography,” he agrees. “And she only ever defends. So there is something in that.”

Inevitably, the studios have come calling for Jones. He has turned up in both The Hunger Games and Captain America films, but he still finds time to appear in minutely budgeted projects, such as last year's superb By Our Selves.

In Captain America he shouts at enormously expensive collapsing buildings. In By Our Selves he discusses John Clare in a field with Alan Moore. Is there a conscious effort to strike a balance at work here?

“Oh, yes. We all think about what we enjoy most about our job. Don’t we?” he says. “I think the thing I find most glamorous and the most exciting is not knowing what the future holds. It’s the most precarious, horrible thing, but it’s exhilarating.

“There is no special place I’m heading for where everything is lined with Oscars and I am massaged 24 hours a day.”

I’m sure he’ll get there, anyway. “Ha. Well, my job is just to have as rich and varied a time as possible.”