On Sunday morning, for instance, he had Peter Salmon, controller of BBC 1, on the ropes. In front of two hundred or so of the trendy ones, he was indulging in what he might describe as knockabout fun, but for Salmon it must have been a stomach-churning ordeal. Humphrys quizzed him on declining audiences, poor quality drama, and an embarrassing lack of successful comedy.
He did what Radio 4 Today programme listeners love him for - he held on like a puppy biting into a trouser leg, performing with the confidence of someone with 40 years in the business behind him, throwing in a pause here, and a joke there. He charmed, ladling on his endearingly fake self- deprecation. It says a lot for Peter Salmon that he did not get rattled. He too made some jokes.
At the other end of George Street, though, was another festival, not television but books, where navy blue cardigans and floral skirts were more the thing. Retired teachers wandered around the lawns and into the white canvas tents, browsing, as if they had no meetings at all to go to, or commissioning editors to pitch to. The mood was gentle; any conflicts or tensions were out of sight. It was a scene from Modern Times.
On Saturday night, John Humphrys arrived at the biggest tent to talk about his book, Devil's Advocate - and the queue went on for a hundred yards or more. It is this world that Humphrys is keener to impress than the television bosses half a mile away - because, it seems, he is trying to move on from broadcasting into literature. Like a lot of television and radio people, he appears to regard the literary world with some awe. He has always wanted to write - indeed to write a novel - but has only now made the space, or perhaps summoned up the courage, to have a go.
His reaction to the savaging of his book by Observer interviewer Lynn Barber is significant. She describes it as an immensely long whinge about all the things he hates in modern life, from Damien Hirst to AIDS ribbons. Which, indeed, it is. At the sociological level Humphrys is issuing warnings about victim culture and rampant consumerism, about a lack of dignity in a society where old ladies are reluctant to declare their dismay at the table-dancing establishment at the end of the road.
The arguments would doubtless be welcomed by most Radio 4 listeners, and the folks at the book festival - but are also easily dismissed as the misplaced nostalgia of an old chap settling into a grumpy dotage. Humphrys is unperturbed. He says that he was terrified that the book would be deemed to have a powerful argument, but to be written badly. Lynn Barber roasted it for the content, he says, but said it was well written - "I'll settle for that." Views, he is confident about; they are easy. Writing is a great unknown.
He now has to think about what to do next. He might try writing the novel - but acknowledges that if the dream is ever to be realised, then he has to unlearn his writing style. Currently, as you would expect, his written word is just like his speech, and you can hear the cadences of his voice throughout the book. But writing seems the way to go, because it's a challenge and, he says, there are no longer any big broadcasting jobs that he aspires to.
For this reason he is thinking of scaling down his presence on the Today programme after his three-year contract expires next spring. He may retire from the show altogether, but seems to prefer the idea of dipping in and out of it a few times every fortnight. The problem is that that may not be possible - and there is also the problem of having to stay in touch, reading all the papers every day.
On the Today programme he has reached a comfortable stage without, he hopes, being complacent about individual interviews. Brian Redhead used to worry so much, he says, that he would ask not to be told what was on the following day's agenda. Jim Naughtie will often call in to find out about the next morning. Humphrys, these days, takes it in his stride - he doesn't care whether he knows or not. He feels sorry for the new presenters whom the Today programme is currently trying out. With the big interviews, he says, "they are thinking, `Is this the one that will make me or break me?' Terrible."
By writing this book, Humphrys has taken a megaleap. He is, to use popular terminology, asserting his own brand - the brand of Humphrys - over and above the BBC. This is, of course, causing some consternation back at the Corporation. Television bosses say he has become like one of the elder statesmen of broadcasting. Humphrys seems pleased by this. I suppose it's quite nice, he says, if I can say what I think without being sacked.
The transition from clever interviewer to national figure has come relatively recently - and has been helped immensely by his enemies. When Jonathan Aitken famously dismissed him as "rude, interruptive and partisan", there was a surge in audience support for him. Similarly when, in 1993, the BBC's governors decided to bash him and Paxman for being too aggressive, the public responded by voting him one of their favourite presenters and the Today programme promptly bagged a Sony award.
Where the brand of Humphrys goes next, and how problematic that will be for the BBC, is still unknown. He is, he says, still engaged in the process of finding the perfect organic farm to buy - But perfection is always hard to find, and the search is engrossing, so this may take years.
The BBC's big cheeses can only be pleased that he is currently engaged in such a non-political pursuit. Their problems arise when national figures that the Corporation has created weigh in to criticise it - as Humphrys did last week with a scathing attack on the Six O'Clock News. Having gone public as a person with views, he is now "out there" along with Paxman, Dimbleby, Adie and Simpson, able produce newspaper headlines to make BBC policy-makers shudder.