Sir Paul McCartney, who's 60 next June, has just returned from a "bracing late-autumn afternoon horse ride" to his farmhouse in the Sussex countryside. "Just getting the smell of nature back in my lungs again after being up in the city," he explains.
The bucolic image is in keeping with the long-established view of McCartney; a cosy national treasure, the multi-millionaire with the common touch. There are many more comforting images of Paul – the peace-loving vegetarian, the jovial entertainer with the perpetually vertical thumbs, the tirelessly enthusiastic custodian of the Beatles' heritage. When Linda, his wife and partner of 30 years, died of cancer in 1998, he became Sir Paul the grieving widower – a loss recently eased by the discovery of a new young love, the land-mine campaigner Heather Mills.
However, the comments he's made since writing and releasing the single "Freedom", a response to the 11 September attacks he witnessed in New York, have suggested the unthinkable: namely, that the war in Afghanistan is the first conflict supported by a Beatle. When I put this to him, his response is long, tangled, contradictory and finally angry.
"Normally you're a pacifist and you don't want any kind of war at all, but occasionally something so atrocious happens there's gotta be some kind of response," he says. "I'd like to see the bombing stop but what are you gonna do, turn the other cheek? I don't think that is possible.
"When I started getting into thinking like this it took me back to conversations we used to have in the Sixties. All the guys sitting round saying if there was a war we'd be pacifist. But I made one little disclaimer and said, 'But if Hitler was invading, and I had a family, I really would feel I have to do something.'
"I remember people thinking, 'Oh oh, stiffening of resolve here.' I knew it was true, deep in my veins. It's like we used to live with this thing every Christmas in London, where the IRA would say, 'We're doing a bombing campaign.' And we'd go, 'How irksome, I hope it doesn't hit me when I'm shopping.' After the New York attack, my attitude was like, screw you man, just screw you. I've got kids living in London. Are you gonna do a bombing campaign? How dare you? If you want to take my kids out – well, screw you. Come and talk about it, right in my face baby."
The fighting talk may seem out of character, but in his autobiography, Many Years From Now, McCartney revealed that as a child, long before he became a celebrated animal-rights activist, he would hunt, kill and torture frogs in the woods near his home in Speke, Liverpool. So, does he play the drums of war and the pipes of peace? Is he, I suggest, a typical split-personality Gemini?
"The old tortured frog syndrome? You could be right. I didn't have to own up to that stuff – but in my tiny young mind, I knew why I had to do it. We fully expected to have to join the army and be made a man of – that was the phrase. We all dreaded National Service back then; luckily, with the advent of the Beatles, all of that ended – otherwise, those of us that would have been drafted, would not have had a band, no way.
"When I saw army training films of guys running into dummies and bayonetting them, I had a vivid enough imagination to go, 'OK, that's what I'm gonna have to do, run at a guy with a big sword and kill him.' I'd seen enough films to be terrified by that as a kid. The whole idea of the frogs was: let's practise! We'd go in the woods and get a frog; I thought, if I can't kill a bloody frog, I'll never be a man. It was a terrifying bloody thing. I say to people, 'Didn't you do that too?' And they go, 'Noooo, I was at Sunday school.'"
Interviewing Sir Paul, the most striking thing perhaps is not observing how the passing years have affected his doe-like features, but being exposed to those unmistakeable speech patterns. The effacing lapses into colloquial Scouse, the term 'baby', used knowingly in the style of an aged, Austin Powers-style 60s roué, and the liberal use of the F-word. Away from the business setting he seems at ease; his voice is certainly relaxed, even a little slurred. In the past his fondness for marijuana has caused him considerable legal problems. Did he celebrate the recent easing of the law?
"I think it's a good idea, but it just happens to coincide with a period when pot isn't something I do as much any more. Why is that? Because Heather doesn't. I don't want to be sitting there at a restaurant and say, 'Hey baby, I have to run to the bog and smoke a joint.' It just doesn't occur." Another habit he has kicked is cocaine, to which he recently admitted he became addicted in a year-long "binge" before Linda "helped pull me back". "Linda would say, 'Are you sure you want to do that tonight?' And I'd go, 'Oh, is there an alternative?' She reminded me that there was this real life out there that I liked a lot."
In the past the themes of loneliness, love lost and love regained have spurred some of McCartney's greatest songs. While he's the first to acknowledge the futility of trying to better "Here, There And Everywhere", "For No One", "Let It Be" or even "Maybe I'm Amazed", his recent experiences have given the songs on his new album, Driving Rain, a raw emotional edge and open-hearted honesty. As a seasoned craftsman, McCartney knows well, perhaps too well, the tricks and techniques of his trade. But between the opening "Lonely Road", with its explicit Lennon and Linda references, and the raging euphoric 10-minute closer, "Rinse The Raindrops", Driving Rain is soul-baring, metaphor-free stuff. Was this, I ask, deliberate?
"I dunno," he says warily. "That sounds true, but I'm just trying to write a song and it's not that easy. I do draw on things that seem important at that time. But it's like you have a dream: the minute you start analysing it all this extra significance comes out. It's one of the reasons I love doing it: there's a mystery to it. And I've been involved in this amazing succession of mysteries."
Of course, among these mysteries the greatest is still "Yesterday" which, famously, came to him fully formed in a dream in 1965. When the Beatles split Lennon used the song to chastise his former partner in the lacerating "How Do You Sleep?". "I felt deep pain," McCartney says now. "Stick it in the jugular, why don't you, John. The funny thing is later I heard that he didn't write that line, that John, [his manager] Allen Klein and Yoko were sitting round together and someone came up with that line. But it was very painful, a bad period, there was a lot of deep messages in all the stuff we did then. I was really writing a lot of songs to John.
"Then I got this great story, in one of the last interviews John did, where he said this guy brought him a copy of "Coming Up"  and he was, like, 'Bloody hell, Paul's on to something – better go back to work.' You better believe I love that story."
The success of the Anthology series and the recent collection of Beatles' numbers ones proved that nationally, and internationally, the cross-generational fascination with the band is as strong as ever. And no one has cherished their legacy more tenderly than McCartney: the band and his late songwriting partner – despite the cruelty and abrasive putdowns – remain constant touchstones. While making Driving Rain, McCartney tried to recreate the working methods the Beatles used during Rubber Soul and Revolver. "That was the time I remember getting the best feeling of my recording career," he recalls. "By that stage we were young executives, we had the suits, the gear. We were hot."
He says there were good times later, but they were less frequent. "That was the period when the term 'heavy' was coined. I remember Tony Bramwell [of Apple] came to a meeting we were having at Apple, and it was really intense: you could feel a weight in your soul just sitting there...
"But the Beatles thing, the more you review it, the more insane it gets. Those guys did a lot of shit. And I talk about them as if I wasn't in them. Checkpoint Charlie – bing! But it's beautiful, man, so intensely beautiful, magical for me. I'm like a fan, it's not like I can't hear what a fan hears. Sometimes I might get a little drunk, and I hear a moment in a song and I'm like, yesss! I try my whole life to get that note, because sometimes I think we were the only guys that never saw the Beatles."
Lennon came to mind again recently when he embarked on his latest foray into the world of classical music, Ecce Cor Meum, a work in progress he began during his late wife's illness, due to be premiered next year. "John used to say if you get to the edge of a cliff, throw yourself off. I'd say, 'Well no, John, you throw yourself off, and tell me how it is when you do, and then I might follow you.' That was John and me right there.
"But now I find myself accepting an offer to do something with the Liverpool Philharmonic, and then halfway through the sensible me kicks in and I think, this is pretty hard. A serious choral person asks, 'What text are you using?' I go, 'I'm doing my own.' Everyone else has used some obscure French medieval poet who has written great stuff, and I'm thinking I'll make it up. It's weird, it's like going off the edge of John's cliff at last."
Indeed, with George Harrison's treatment for cancer and the recent accusations about the Beatles' treatment of their original bassist Stuart Sutcliffe, the ghosts of the past – and thoughts of death and oblivion – are perhaps looming larger than usual. And it's interesting to speculate what Lennon might have made of McCartney's new-found enthusiasm for war.
But McCartney does have the excuse of having been in New York not just for the 11 September atrocity but also for this week's air crash – a coincidence that prompted a horrible sense of déjà vu. "I looked out the window and saw smoke and thought, 'Oh God, not again'. It was like the twin towers all over again." Perhaps even the pacifist Lennon could understand that.