LONDON – It doesn’t take much to set Noel Gallagher off. We are sat in a backstage portacabin at London’s peculiarly ragbag Clapham Calling festival, and I’ve just mentioned to the former Oasis songwriter that “Chasing Yesterday,” the second solo album under his High Flying Birds banner, is the U.K.’s fastest selling of the year.

“Is that impressive? I’m not impressed by it! I’d rather be the biggest selling,” he says. “The fastest selling, what does it mean? It means that if you put my CD on a table with Muse’s and Florence’s, it would win in a race to the end of the table. I don’t know what it means. Let me tell you — I’d rather be the biggest selling.”

You’d expect nothing less from Gallagher, Manchester’s great motormouth and a man whose ambition, stretching back to Oasis’ fledgling days, was always to obliterate the competition, musically and verbally, into irrelevance. He told everyone who would listen — and especially those who wouldn’t — that Oasis, fronted by brother Liam, would be the biggest band in the world and he was right: In the hedonistic Britpop era, Oasis didn’t as much catch the zeitgeist as set fire to it, first with its fantastic 1994 debut “Definitely Maybe” and then with the 22 million-selling follow up “(What’s the Story) Morning Glory.” With his anthemic rock ‘n’ roll tunes, Gallagher mastered the trick of writing songs that ostensibly said nothing but meant everything, and his resolutely working-class Mancunian outlook of hope and camaraderie found a universal audience.

“I think we accidentally connected, somehow, through magic, with a whole generation of people all over the world,” he says.

The memory of just how huge Oasis was remains vivid even two decades later: every raucous gig, every outlandish interview, every brotherly argument, all events in themselves. The band’s pinnacle, playing to 250,000 people over two nights at the Knebworth Park Festival in August 1996, was a high (in all senses of the word) that Gallagher, in his more fanciful moments, wishes could have been a glorious finale.

“It would have been like the greatest thing of all time. But what would I have done?” he says. “I was in no way ready to be what I am now back then, no f—-ing way. I couldn’t sing then. I could barely do backing vocals. I was a drug addict. There was no way it could happen. We would have been cast to the wind.”

He leans back and smiles mischievously: “It would have been handy if somebody had died. We could have called it a day then.”

Nobody did, and the bloated, cocaine-ravaged mess that was the third album, “Be Here Now” (“it’s awful, I can’t listen to it”), came to exemplify the era’s garish excess. By 1998 Britpop had eaten itself, leaving Oasis to carry on regardless, ever popular yet with the magic intermittent, albums patchy and the friction between Noel and Liam increasing.

When Oasis finally imploded, it was spectacular. A still unspeakable altercation with Liam in a Paris dressing room in August 2009 was one fight too far, making rock’s great sibling rivalry untenable and bringing Oasis crashing to a halt. It always seemed inevitable the hostility between the pair — Noel the talented songsmith stage left, Liam the charismatic, handsome focal point with the thrilling Lydon-via-Lennon snarl — would lead to Oasis’ downfall. Wounds are far from healed.

“I don’t know anything about what he’s up to,” he says of Liam, now of no fixed musical abode following Beady Eye’s split. “I’m not his keeper anymore. Whatever he does now is his business. I really don’t give a f—-.”

Predictably, their relationship is invariably viewed through the prism of the band — Gallagher bemoans that he “answers questions about reforming Oasis every f—king day” — but given there’s no immediate chance of that happening, I am more interested in the personal aspect: Is there no part of Gallagher that feels sad at the very public, complete breakdown of his relationship with his younger brother?

“Yeah yeah yeah, oh f—- yeah. In a way, yeah,” he says, for once seemingly unsure of what to say. “But let’s not forget — he is a c—-. He’s not a very nice lad. And that is the basis of it. It’s not like he’s the perfect gentlemen and unfortunately we haven’t been talking. It’s not like that. For that band not to be together, the band that we all love and that we started, something f—-ing serious happened. I’m not going to go into it.” He puffs out his cheeks, exasperated. “But I don’t care anymore. I’m too far gone into this now to care about what he’s up to or what he’s doing.”

That’s not to say Gallagher doesn’t occasionally think about what he has lost.

“I do miss just being a guitarist and standing on that side of the stage being at an Oasis gig with the crowd, because I was observing it going on as well. It might be nice to be in a band one day. But let me stress,” he says, leaning forward and pointing, “it won’t f—-ing begin with the letter ‘O.’ ”

Gallagher can afford to be so dismissive. His unfailingly forthright tongue might suggest otherwise — “Who wants to listen to a world radio station? Who cares what some f—-ing lunatic is listening to in Korea?” is his take on Apple’s new streaming service — but at 48, he doesn’t need the hassle (or the money) that would come with an Oasis reunion. Besides, the High Flying Birds have taken off: The eponymous debut sold 2.5 million copies, over 70,000 of which were accounted for in Japan.

With “Chasing Yesterday,” he even provides a riposte to critics who say his music remains unnecessarily conservative. Oasis-style rock anthems are present and correct, but there are also hints of prog, saxophone and on one song, “The Right Stuff,” Gallagher even dabbles in “space jazz.” It’s a song he wouldn’t — or perhaps couldn’t — have written 20 years ago.

“Oh for sure,” he says. “If you were to put ‘The Right Stuff’ on a compilation of my songs straight after (1994’s) ‘Supersonic,’ you’d think it doesn’t sound like the same songwriter. I would never have got to write that song when I was in Oasis. We were a rock ‘n’ roll band, we were very aware of what we were and there wasn’t really any room. Imagine playing ‘The Right Stuff’ at Wembley Stadium in front of a bunch of fat skinheads? I don’t f—-ing think so.”

There is a sense that Gallagher should make such musical exploration a habit. ‘The Right Stuff’ was a result of his much-discussed, controversially abandoned project with pioneering dance producers Amorphous Androgynous — “I’ve destroyed the masters, it wasn’t good enough, that’s it” — yet the track is undoubtedly one of Gallagher’s best in years. Perhaps he’s taken note: after a rumor he inadvertently started himself during an interview on Dutch radio last month, he admits interest in collaborating with Jamie xx.

“I do actually own a couple of his singles and I would work with him,” he says. “But he most probably thinks I’m s—t, so we’ll leave it at that.”

The immediate future is Gallagher’s closing set at this weekend’s Fuji Rock Festival. The musician has played at Fuji Rock four times, including a headline slot for Oasis in 2009 when the band was just three shows and one month away from collapse: A world away from Oasis’ first trip to Japan in September 1994, the month after “Definitely Maybe” was released.

“I remember it being the first experience of the mania,” he recalls. “We were the hot s—- in England at the time, we went to Japan and there were thousands of kids outside the hotels and you couldn’t move, you couldn’t go shopping, couldn’t do anything. We were there for two weeks and we experienced this Japanese mania and by the time we got back it had caught on in England. And then for a good few years it was like that everywhere we went. But I remember the Japanese were the first to go truly mad and it was great.”

As the packed field at Clapham Common later proves, people are still going mad for it: the Oasis songs that pepper Gallagher’s show are bellowed back with life-depends-on-it commitment, often by those not even born when “Wonderwall” was inescapable and Gallagher was fulfilling his rock ‘n’ roll dream. It’s a source of great pleasure for him.

“What surprises me now is that after all these years I can do a gig and play six Oasis songs, only one of which was a single, and people know them all over the world. I don’t know another living band, apart from The Beatles and maybe the Stones, that can play a b-side unannounced in the middle of wherever and it be treated like a huge song. So that makes me feel proud. And people still love it. They still love the songs.

“Which is handy for me,” he says, “because I f—-ing wrote them all.”

Noel Gallagher’s High Flying Birds headline Fuji Rock Festival on July 26. The festival takes place July 24, 25 and 26, and will be held at Naeba Ski Resort in Niigata Prefecture. A one-day ticket costs ¥16,800 and a three-day pass costs ¥39,800. For more information on the artists playing, visit www.fujirockfestival.com.