As the man who penned When I’m 64, it probably goes without saying that Paul McCartney felt a twinge of trepidation as June 18, 2006, finally approached. The way McCartney tells it, the plan was to pay little attention to it, perhaps avoid going out of his way to hear his most vaudeville contribution to Sgt Pepper. But that very morning he was greeted at his house by a delegation of younger McCartneys. “My kids did a version for me,” he exclaims from the kitchen of his Sussex recording studio. “I even had the baby doing it.” By way of illustration, McCartney lets forth a high-pitched imitation of Beatrice Milly McCartney singing When I’m 64 with atonal gusto.

A prurient inquiry springs to mind at this point. You wonder if Heather was there, singing along with the Maccas, all the better to imagine the atmosphere on that mildly mythical morning. But you weigh up the risks of upsetting a Beatle and you let it pass.

By the time he reached a pensionable 65 this year, he had turned into another one of his songs – he was here, there and everywhere. No doubt, some of the attention was unwelcome. When redtop headlines weren’t trumpeting the latest instalment of his divorce they were shining a light on his ensuing liaisons – a weekend apparently spent with the Hamptons socialite Nancy Shevell, and his current relationship with Rosanna Arquette. But even setting that aside, it was a period of activity unseen since the days when he had three other Beatles beside him to share the burden.

In June he formally severed his 45-year relationship with EMI by releasing his 14th solo album, Memory Almost Full, not with a conventional record label but with Starbucks’ music division Hear Music. Along the way, there were British and American gigs of hysteria-inducing intimacy and even a measure of acceptance for his classical work – his memorial piece to Linda McCartney, Ecce Cor Meum, earned him a Classical Brit.

During a 50-minute conversation, there is one word he uses more than any other. If, as GQ recently declared, Paul McCartney is the Man of the Year, then “exciting” was his word of the year. And if something wasn’t exciting, Macca didn’t want to know about it.

It seems that excitement – or rather the lack of it – struck the death knell for what was already becoming a strained relationship with his old label. “Everybody at EMI had become a part of the furniture. I’d be a couch; Coldplay are an armchair. And Robbie Williams, I dread to think what he was,” he begins. “But the most important thing was, I’d felt [the people at EMI] had become really very boring, y’know? And I dreaded going to see them.”

Boring in what way? “Well, because I could guess what they were going to say – ‘Love your record, Paul’ – and I’d say: ‘Well, what should we do with it?’ Then they’d go: ‘Well, we think you ought to go to Cologne’, which is what they always say.

“This idea became symbolic of the treadmill, you know? You go somewhere, speak to a million journalists for one day, and you get all the same questions. It’s mind-numbing. So I started saying: ‘God, we’ve got to do something else’.”

Had his American producer David Kahne not been on hand to hear these grievances then McCartney may never have got as far as working out what that “something else” was. Unluckily for EMI though, Kahne had friends at Hear Music. By the time McCartney got around to telling EMI the bad news, the deal was as good as done. Someone at the coffee chain told him that 400 Starbucks in China would be stocking the CD. He liked the idea almost as much as the fact that no one had mentioned Cologne.

The clincher, though, was the meeting he had with Starbucks executives, in which Memory Almost Full was played back in its entirety. “You Tell Me came on and one of the team started crying. It was weird. I thought, ‘Oh, this is real feedback.”

Not much crying at EMI then, lately? “Well, there is, but for other reasons,” McCartney says. It might be argued that, for an industry monolith such as EMI – now owned by a private equity firm, Terra Firma – losing Paul McCartney in one year is unlucky. That the label went on to lose Radiohead because, in the words of the guitarist Ed O’Brien, “Terra Firma doesn’t understand the music industry” – starts to look like recklessness. Thom Yorke may bristle at the idea of jumping ship to Starbucks, but one thing he and McCartney have in common is their enthusiasm for new, faster ways of putting out music.

Actually, they’re strangely reminiscent of the old ways. McCartney was one of millions who downloaded Radiohead’sIn Rainbows, paying “something reasonable”, on the week it appeared. “This was how we used to operate,” he enthuses. “I remember John [Lennon], for instance, writing Instant Karma and demanding it was released the following week.”

It wasn’t the case with EMI. “I’d started saying to them: ‘Look, we could write a thing and have it released the next week.’ And they would say: ‘You can’t do that these days.’ So I would say: ‘Well, how much time do you need?’ And they’d say six months. I said: ‘Why do you need that long?’ And do you know what they said? ‘To figure out how to market it.’ I said: ‘Wait a minute, are you sure you need six months for that? Couldn’t some bright people do that in two days?’ Jesus Christ. I said: ‘Look boys, I’m sorry, I’m digging a new furrow.”

And a fertile one at that. This year he bought the domain name www.meyesight. com (a pun on MySpace but pronounced so that it rhymes with “eyesight”) as a platform for his poems, paintings and demos. Far from making him retreat behind locked doors, the fallout from his divorce from Heather has thrown him not just into work but into a whirl of social engagements. At the Q Awards in September he got talking to Damon Albarn and congratulated him on the success of his Africa Express “super-jam” at Glastonbury.

“He asked me to take part in it, actually. I couldn’t do it because of my personal difficulties. I was looking after my daughter and I couldn’t really schlep her down and do that. But I think they’re gonna do another one, so I might get involved next year.”

The way his 2008 is shaping up, McCartney might find it no less of a struggle to fit in the next one. In February he picks up an award for Outstanding Contribution to Music at the Brits. Between then and his Anfield stadium show in the summer, he goes into the studio to assist on an album of songs by his famously shy son, James.

Also nearing completion are a guitar concerto and a new album under his nom de plume The Fireman. While he’s under no illusions about the place these projects will have in the mainstream, you suspect that much of his current swagger stems from the reception accorded to Memory Almost Full. It’s a record on which the Linda years seemed to loom large – not just on Wings-style rockers such as Only Mama Knows andNod Your Head, but across a succession of confessional, contemplative songs. Writing about his happiest years as though part of some increasingly intangible dream,You Tell Me, That Was Me and The End of the End numbered among his most affecting tunes for years.

That McCartney takes as much inspiration from Wings these days as he does from the Beatles, is probably no accident. The Beatles don’t need anyone to stick up for them. But the same can’t be said of the band formed by Paul and Linda in the hangover of the decade that the Beatles helped to define. When talk turns to the subject of Wings, McCartney relays a favourite story about Bruce Springsteen. “We were at the Rock ’n’ Roll Hall of Fame and we got talking. He said: ‘You know what? I like Silly Love Songs. I really didn’t get it at first, but now I’ve got a wife and kids I get what you meant’.”

It isn’t difficult to work out the subtext of this story. Having spent the Sixties as you would expect a Beatle to spend the Sixties – seeing Jane Asher, getting high with his arty mates at the Indica Gallery, being a Beatle – he changed with the new decade.

And many of his contemporaries resented him for it, little realising that the changes he underwent would befall them too. Family. Kids. Mellow times. “Some people wanna fill the world with silly love songs/And what’s wrong with that?”

Does he ever get bored of being portrayed as easygoing, thumbs-aloft Macca? I suggest that his glass-half-full persona must have been manufactured as a method for coping with his extraordinary fame. He bristles slightly at the word “manufactured”. In fact, he says, it was probably a mechanism that activated itself during an adolescence overshadowed by the death of his mother. “If you knew anyone I went to school with, it was the same, you know. I was pretty optimistic.”

Besides, even happy songs have a way of turning sad as the years go by. Penny Lane pauses the videotape of memory on a moment to which its author knows he can never return. Even When I’m 64 carries a poignancy that he couldn’t have foreseen when he wrote it. “You know, I think you’re getting to the philosophical core of things when you say that. Things that are happy also contain the seed of sadness.”

By way of illustration, he pretends to be a brass band playing I Do Like to be Beside the Seaside. Images of Victorian ghosts in stripy bathing costumes suddenly abound. “See what I mean? One day, when we discover the meaning of life, that will somehow be contained within it – that happy is sad and sad is happy.”

At the risk of sounding like an enterprising Starbucks executive with a chopped onion secreted in his handkerchief, I tell Paul that the home movies on The McCartney Years – a new DVD anthology spanning his work with and beyond Wings – movingly underscores the point. Particularly affecting is the footage of the McCartneys revelling in anonymity at their Scottish farm retreat. It must have been incredible to raise children who had yet to rumble who exactly their dad was.

“Exactly,” he says. “There was one moment where they were riding their little ponies in Scotland, and Stella said to me: ‘Dad! You’re Paul McCartney, aren’t you?’ ‘Yes darling, but I’m Daddy really’.”

Were any reminder needed that he’s still Daddy, he has to leave his studio in a few minutes to pick up four-year-old Beatrice from school. On the way back they might do some Christmas shopping – a ritual with which he is quite hands-on. “I like to do that myself, you know?” In terms of getting the kids excited, I tell him I can recommend the Argos catalogue. It’s got nearly 2,000 pages.

“I don’t get the Argos,” he says, with the mock air of a man who may yet do – now that the idea has occurred to him. “But I do have others. There are catalogues that are even better than Argos. Believe you me.”

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