"Radio," says Jim Broadbent, "has the virtue of purity. It's comfortable to perform in, even relaxed, which is not generally the case with film and TV. You haven't got a film crew hanging on your every word, nor have you got that terrible adrenaline fear that you get before going on stage."
"Another appeal," he admits with a mild laugh, "is that you don't have to learn the lines. And the BBC is very experienced when it comes to choosing the right people for the production."
Radio likes him back and back he has duly come, just completing work on a Words and Music programme for Radio 3. It's called The Full Montaigne and is based on the writings of the 16th-century French essayist Michel de Montaigne. Broadbent's involvement with the BBC's original medium can be traced to near the beginning of his 40-year career, in the days when he still called himself James, rather than Jim.
"It's quite hard to remember everything you've been in on radio," he admits, "because you haven't had it imprinted into you as you do when you've learnt the lines. But I do remember being in The Hitchhiker's Guide to the Galaxy, although not in a big part, back in 1977. I was also in a Week Ending, but I wasn't very good. David Jason had dropped out so I deputised for him. It was produced by Griff Rhys Jones, so that dates it."
There was also a radio production of Greatest Story Ever Told, by the National Theatre of Brent in 1996. That went out live, didn't it? He remembers with a wince that it did and that it was one radio experience that was at least as frightening as the stage.
The Full Montaigne is Broadbent's second Words and Music, the first being 2010's equally chewy Doors of Perception. It finds him in the role of a writer and thinker noted for his humane and deceptively simple reflections on the conduct of life. It was not until nearly a century after his death that the Vatican discovered Montaigne's unpalatable statements that death is merely the end of life, and that humans are not superior to other animals, and put his essays on its list of prohibited books.
No wonder the atheistic Broadbent admires the writing, which is radical, witty and plain dealing. "It's very stimulating to find the 16th century resonating so clearly with the present day," he says. But, how to be Montaigne, that is the question: how to represent this foreign man from a foreign time. The trick, he explains, is simply to try and understand and present the story that Montaigne is telling, and at all costs not to interrupt.
Up strikes Boccherini's sprightly Fandango (Quintet No 4) as a soundtrack behind the essayist's bleak vision of love, which he describes as "Nothing but the thirst for sexual enjoyment in a desired object." As for marriage, Montaigne sees "None that sooner are troubled and fail than those which progress by means of beauty and amorous desires."
From sex to gender Montaigne sounds resolutely modern: "Women are not wrong when they reject the rules of life that have been introduced into the world in as much as it is the men who made these without them."
Montaigne isn't always easy to follow. "There were some constructions where I found it quite hard to tease out the meaning," Broadbent admits, "and where I wasn't sure if I got the right message from them". But radio's simplicity, he feels, can be a positive advantage when it comes to conveying a character, since the listener's imagination is invoked without the interruption of visual images.
Broadbent is, by his own admission, more of a music lover than a concert-goer. His wife, the painter Anastasia Lewis, usually picks the concerts, and he tends to prefer familiar works, or those by well-known composers.
But switching on the radio is something he does all the time. Yet it turns out he is not one of those listeners who has a default setting in their own wiring, taking them back to the station of choice. In fact, he is precisely the opposite, the only consistency being that all the stations he mentions are BBC ones. "There's so much of it," he says. "I don't sit down and listen to something from start to finish, but you pick up on what's there. It's the whole eclectic range that appeals to me - the comedies, the dramas, the documentaries, the news, everything really. Oh, and the world music programmes on Radio 3."
Coveted by directors for his subtle virtuosity, most recently as Denis Thatcher in The Iron Lady, the Bafta and Oscar-winning actor shares his profession's uncertainty about what's coming next. However, he has something in the offing that he says could be "very exciting." He is also part of a distinguished cast (including Tom Hanks, Halle Berry and Hugh Grant) for a film version of David Mitchell's 2004 novel Cloud Atlas to be released later this year. And he has recorded, as an audiobook, Rachel Joyce's novel The Unlikely Pilgrimage of Harold Fry. "A marvellous book," he says, "but very demanding. A marathon."
Words and Music is on Radio 3, Sunday at 6.30pm