One of Peter Hall's first actions on founding the RSC in 1960 was to invite a junior don from King's College, Cambridge, John Barton, to join him as an associate. Forty-six years later Barton, despite a falling-out with Hall, is still there as an "advisory director" and, at 77, is busier than ever. As we met, he was preparing a one-night production of his anthology, The War That Still Goes On, revising the proofs of a new edition of Tantalus, and getting ready for the RSC's forthcoming Shakespeare marathon. He was even keeping an eye on Celebrity Big Brother.

Barton is a man around whom legends accumulate. As a young director, he reportedly chewed razor blades during rehearsals to concentrate. Once, he was so absorbed in giving notes to actors that he fell backwards off the stage into the orchestra-pit, whereupon he dusted himself down and instantly resumed. Yet nothing could be further from the truth than the idea of Barton as an academic eccentric at large in the rough world of theatre. He has directed some of the greatest Shakespeare productions of our time. His TV series, Playing Shakespeare, became an instant classic. And he is surprisingly conversant with TV soaps, and is angling to get George Galloway to join the debate that will follow The War That Still Goes On on February 12.

The show itself is an anthology drawn from Thucydides and Plato, and has a long RSC history. "It was first done in 1967," says Barton, "as part of a fortnight exploring Greek myth. It was then televised and later revived during the Gulf war and it seemed opportune to bring it back now. It's absolutely not about Bush and Blair. It's a timeless text that always seems relevant to the moment. About three-fifths of it comes from Thucydides's History of the Peloponnesian War, the rest from Plato's Socratic Dialogues. But a large part consists of debates about war which Thucydides reports from memory. The result is not a political diatribe. It's really an examination of a particular war that suggests that what has happened in the past will happen again and may be of some use in the future."

Even if Barton disclaims any propagandist intention, he believes that the crux of the evening will be the ensuing debate. "When we first did it," he recalls, "Enoch Powell and Tony Benn took part. Benn was very enthusiastic and said the text should be in every school curriculum. Powell was very laidback, runic and quizzical. I was in awe of him because he was a professor of Greek whereas I'd done my dissertation on Beowulf. Hearing this, the actor playing Socrates said incredulously, 'You did a dissertation on werewolves?' But I remember at the end someone asked Powell if he thought democracy would last. He paused a long time before replying, 'It's much too early to say.'"

This time Barton is going for broke. Jon Snow will chair the discussion with Paul Cartlidge, a Cambridge Greek scholar, and Germaine Greer among the participants. "I've known Germaine," says Barton, "since my wife supervised her at Cambridge. But I've probably put my foot in it by asking George Galloway. I've watched him on Celebrity Big Brother and I'm impressed by the way he goes along with all the games and listens to people. He strikes me as very intelligent, lucid and laidback and gave a brilliant Shakespearean performance in front of the Senate committee. But I also want to have a hawkish American neo-con like Paul Wolfowitz so we can get a serious debate going."

That, if nothing else, should dispose of the notion of Barton as an unworldly academic. But, for all his immersion in classical legend, Barton points out he has never directed a solo Greek play. In 1980, he staged a magnificent 10-play cycle for the RSC, The Greeks, that told the unfolding story of the Trojan War. And in 2000 his epic, Tantalus, memorably completed the myth. But Barton explains that this is simply an extension of his long-term interest in narrative sagas.

"As an English scholar," he says, "I studied Anglo-Saxon and became fascinated by the Norse Sagas and the idea of telling a story through character and speech. When I was at Cambridge, I did a 12-part series for BBC radio on the medieval Mysteries; but any hope of doing them on stage was destroyed by Bill Bryden's version which was one of the greatest things I've ever seen. Later on, I had a scheme to do the Napoleonic Wars at the Barbican, complete with the battle of Waterloo, but that never happened. But The Wars of the Roses, which I edited and co-directed with Peter Hall, stemmed from my love of narrative. And, when I want to escape the horrors of the world, I watch The Bill on television. It's not a soap but it's very well acted, cunningly plotted and follows continuing characters. I'm not so much into Coronation Street and EastEnders: I get them muddled up. But much of my working life has been governed by a quest for epic narrative."

Tragically, however, Barton's last big project, Tantalus, has left unhealed scars: dealing with the origins, climax and aftermath of the Trojan war, it led to a Homeric row when Peter Hall removed one of the original plays and tightened the narrative structure in advance of the Denver premiere.

"It's a totally unresolved matter," says Barton, "and a source of great sadness. Peter won't meet and talk to me about it, and it upsets me deeply after a friendship of 50 years. I wrote the bloody thing. I said to Peter, 'I don't know if it's any good but, until you run it through, I won't know what to cut and adapt.' I think the truth is that, once Peter started doing it, he lost confidence in it and felt it wouldn't work; at which point I should have told him to drop it. But he put it into masks when he'd agreed it wasn't a mask-play and changed it to a one-day event when I always felt the story needed two days to unfold. When I saw it in Denver, I was very diplomatic because I didn't want to attack it while the actors were still doing it. But, although I've tried to extend an olive branch to Peter, I've only got a tart reply. It disturbs and upsets me because I've known him since he was so high. At our age we ought to be able to chuck the odd brick at each other and get over it."

Even if the breach with Hall remains unhealed, Barton has enjoyed a fruitful relationship with successive RSC directors: Trevor Nunn, Terry Hands, Adrian Noble and now Michael Boyd. Having worked his way through much of the Shakespeare canon, Barton now spends his time advising everyone else: holding regular verse-speaking surgeries with young actors and offering counsel to directors on specific productions. But doesn't that become difficult when, like Barton, you yourself have done near-perfect productions of Twelfth Night, Love's Labour's Lost and Richard II?

" I do get protective," admits Barton, "over certain plays, so I will only intervene when asked. I talked to Trevor a lot about Richard II before his Old Vic production but, from what I read about it, I felt it probably wasn't for me. I think Trevor's one of the best directors alive but I felt what I had to say afterwards wouldn't be valuable and might even be offensive. But, while I don't want to be a spectre haunting the RSC, I try to be of help. I'm very close to Greg Doran and told him, after I'd seen his Midsummer Night's Dream, that I found it over-inventive and a bit inhuman in places. We had a very open, civilised discussion about it and I think Greg went back and changed certain details. So, although I'm an advisory director, I only try and offer advice when it can be of use."

What is hard to gauge is the influence Barton has had over the RSC. But my guess is that its survival over the last 46 years owes a vast amount to his practical wisdom and sage counsel. He has been the resident guru to a variety of directors, though he modestly disclaims being the secret of the company's longevity.

"If the RSC has survived," he says "it's partly due to the luck of the gods. I think if you'd asked Peter or Trevor whether it would have lasted into its fifth decade, they would have said it was very dicey. It was never wanted by the establishment. But that may be one reason for its astonishing tenacity. Whatever the achievements of individual directors, I also think the success or failure of the RSC depends on the quality of the actors. If I've learned anything in my time, it is that if you get the right combination of actors, a production will generally work. Which is why I'm cheered that the new season will contain a lot of experienced names - like Patrick Stewart, Harriet Walter, Judi Dench and Ian McKellen - as well as brand-new faces. But one should always remember that no theatre company is immortal and Zeus could still chuck a thunderbolt at any moment."

So saying, this kindly, cardiganed Richelieu goes off to attend to the business of war, the hunt for an American hawk and the eternal pressures of a new Stratford season.

· The War That Still Goes On is at the Novello Theatre, London WC2, on February 12. Box office: 0870 950 0948.