Liam Gallagher is a bagful of energy. We're sitting in a back room at Selfridges department store, where later he'll sign autographs for people who buy T-shirts or parkas from his Pretty Green clothing range, and as we talk he continually stamps his foot - clad in his own-brand desert boot - as though to an insistent, unheard, drumbeat.

Sometimes he leaps up and performs a little mime as he answers a question. And sometimes, so obviously full of anger is he - cursing and gesticulating and bunching his fists - I genuinely fear that he's going to kick a posh leather chair or punch a hole in the wall.

Or maybe I misread him. Maybe he's just very excited. Because Gallagher is at his most animated when he's talking about the new album Oasis will record after Christmas - without his older brother Noel.

Branching out: Liam Gallagher wears paisley pattern shirt, £180, from his new menswear collection

"We're halfway there, man," he cries. "We've got all the songs done. Without Noel at all. Me, Andy and Gem [Oasis bassist Andy Bell and guitarist Gem Archer] are doing it. That was the way it was going anyway, even on the last record.

"We were, like, doing most of it and Noel was off doing his own thing. So we've got a bit of studio time booked after Christmas and we're going to get in there, do it quick, with no stewing on it, and I'm feeling really confident about it."

And this, of course, is hugely intriguing - a new album without the band's supposed creative force? Oasis without Wonderwall or Live Forever?

But let's get old business out of the way first. It was in August this year that Noel Gallagher appeared to make his final, final, exit from the band, after a bust-up backstage in Paris that resulted in the smashing of a guitar and an apparently irrevocable exchange of words. The brothers haven't spoken since.

The marriage: Liam with former All Saint Nicole Appleton, mother of his younger son, Gene

Yet Liam dismisses the scale of the row as a premise for the split: "It wasn't a big thing for me. I've had bigger arguments with me toenails, you know what I mean? I think he just wanted out.

"He'd had enough of this lad thing, and he wants to try something new, and it's not having a dig at him, but I just think he's sort of turned himself into a f***ing fake.

"You don't have 18 years of giving it all this, and then wash your hands of it and start going out with Russell Brand, and all these new pals. I think he's done a Keegan."

Meaning, I think - and this is guaranteed to irritate his brother hugely - that Noel has, as Kevin Keegan supposedly did, walked out on a job without a proper fight.

But the fact that Liam is here, giving this interview as Selfridges officially launch es its Pretty Green concession, and commenting so freely on Noel, is bound to anger him even more.

Liam's voice is suddenly sarcastic: "That's all right - go out and do your own thing, but I'll be keeping it real."

Though others have accused Liam of divisive, prima donna-ish behaviour, he says himself that Noel had "kicked the doors wide open" and invited into the band's inner circle "a lot of newies", including journalists, "who were rude and disrespectful".

It sounds as though Liam felt he was losing control of the band's direction, or perhaps his place at its very centre.

But why is he still so furious? One muso school of thought has always maintained that, for all their high-profile bickering and nasty name-calling, the Gallagher brothers are actually far closer than the average sibling pair, and need each other much more than they'll ever publicly admit, both personally and musically.

The double-act: Oasis's amazing success was built on the combination of Noel's songs and Liam's voice

"I don't think he thinks that," growls Liam. "He's got lots of people around him giving him false pretences ..."

But of course it can't really be disputed that Oasis's extraordinary worldwide success of the mid-Nineties was built entirely on the dynamism and combustibility of the Gallagher double-act: Liam's voice and charisma coupled with the essential beauty of Noel's songs.

But wait ... um, Liam does dispute it. "Listen, I loved it all. I loved Oasis. I love making records. This is what I do, it's an addiction. It's something you've got to perfect and something you'll never perfect.

"We'll make this [new] record and see where it goes and hopefully it'll put a few dickhead [myths] to bed, about who was what and what was what ..."

Later he says: "People are saying: by rights, you should be putting your feet up and counting your money, but that's not my thing.

"Someone has left the band and I need to go out and prove ..." He hesitates, aware, I think, that he's making himself vulnerable here by admitting Noel's obvious influence. "No, not prove," he goes on. "Not prove anything. I mean, I don't want people who supported our band to think I'm just sitting here doing nothing.

"Obviously it's going to be different without Noel and Noel's fans will sneer at it but then, you know, if they don't like the music, don't f***ing buy it. Don't come to the gig, cos you're not going to be hearing Don't Look Back in Anger ... But I do like to think that the 250,000 people who came to see us at Knebworth didn't come just for Noel."

Good old days: Oasis in 2006: from left to right, Gem Archer, Noel, Andy Bell and Liam

And he's right - they didn't come for Noel. They came for Liam singing Noel's music.

But if Liam can pull off a musical re-invention, Oasis can survive. Oasis without Liam, on the other hand - that gravelly snarl, that big physical on-stage presence - wouldn't work at all.

He isn't sure yet whether the new album will come out under Oasis's name or not. "We're not using it at the moment, but if we don't come up with something else by the time we're ready to release the album it'll be Oasis.

"I'm not going to call myself something ridiculous just for the sake of it. We're trying lots of new names right now, but nothing's sticking so we're just plugging on with the music. Obviously we won't be playing any of Noel's songs."

So what's the new stuff like? A radical departure? That, surely, would be the bravest way to go. But: "Nah, not radical. No way, man. It's a little bit different, but not too much. It's the kind of music our fans have always liked, you know? But we'll see. I'm not forcing this down anyone's throats. That's not good for the soul."

And these days, Liam is into soul-cleansing. At 37, he looks pretty good - fit and healthy and smooth-complexioned - despite almost two decades of Oasis and its associated hardcore partying.

We are here to talk not about the band but about his clothes, a range of quality menswear, clearly but not slavishly, inspired by mod culture: parkas in green and ivory, polo shirts, pea coats, and a beautiful soft-as-butter collarless leather jacket for £1,000.

Yet when a Selfridges salesperson mentions that someone has bought a single example of every piece available, spending in the process a sum well in excess of £5,000, Liam instantly assumes it must have been Noel.

"That'll probably be our kid, then. I hear he's been in here having a nosey at it, cos someone caught him and asked if they could help him, and he gave them a dirty look and walked off."

But surely it's more likely to have been a well-heeled fan who just really likes the clothes? It's almost as though Liam can't stop scratching at the sore caused by his brother's antagonistic departure.

Liam's day is dictated not by fashion or rock stardom, however, but by the school run, which he does almost every day.

His boys, 10-year-old Lennon (from his three-year marriage to Patsy Kensit) and eight-year-old Gene by his wife, the former All Saint Nicole Appleton, go to the same private school in Hampstead, and he sees Lennon for a day a week and every other weekend. "I buzz off 'em," he laughs. "They're my heroes, man."

His own father, a notoriously violent man whom his mother left when Liam was 10, used to wear Pierre Cardin while leaving his three sons in scruffy hand-me-downs.

"He was pretty stylish. But all his money went on him, he never gave any to the family ... We'd all go to church in matching jumpers knitted by me mam. We looked like Jedward."

Yet Liam admired his dad's "style", and as a teenager got into the football-led "casual" look - Tacchini tracksuits, Lacoste jumpers, Dunlop Green Flash.

Of course his own children have full-to-bursting wardrobes of their own, though "They're not like the Beckhams' kids, man" and aren't dressed head-to-toe in designer gear. They do own two "little parkas", though, especially made for them by Liam's Pretty Green seamstresses.

Liam claims, then, that "life is good". "I'm buzzing. I'm happy. Dead happy." But he'd be happier with Noel back in his life, right? Wrong.

He leaps up, instantly furious. "I'm sure he thinks: I'll do my solo career and if it doesn't f***ing pan out the way it's expected to pan out, then I'll give our kid a ring cos he'll be desperate, and he'll do anything for Oasis.

"Well, I'll say this right now: he's got another f***ing think coming. If he thinks he can ring me up at any given stage in his f***ing lifetime, I'll be busy. I'll always be busy when he rings me up." He pauses, grins sharkishly.

"You can tell I get agitated by all this. Look, I'm just going to keep me head sane with the clothes, the new record and the band ... Whatever the f*** we're called."

Pretty Green menswear from Selfridges and www.prettygreen.com.