"Maybe After Christmas, we'll Start Banging out Some Tunes"

I wonder how Liam Gallagher might have responded if, a decade ago, he was told that in 2009 he would be giving an interview in which the journalist had been specifically instructed not to ask him about Oasis. It is, after all, the band which defined 1990s Britpop and, in the public's eyes, defines Liam Gallagher.

And, after 18 years, it is no more. On 28 August this year, Liam Gallagher had the latest in a long line of fights with his older brother and fellow band member, Noel, just minutes before the band was due to go on stage in Paris, and the gig was cancelled. Two hours later a statement from Noel appeared on the band's website: "It's with some sadness and great relief to tell you that I quit Oasis tonight … I simply could not go on working with Liam a day longer." There has been very little since by way of an explanation, or hints as to what either Gallagher might do next.

Today I'm meeting Liam for a drink in his local boozer in Hampstead on the premise that I am not to ask him any questions about Oasis, Noel or the split. So what exactly can we talk about? The answer is the Oasis frontman's clothing line, Pretty Green, which he developed this year alongside British tailor Nick Holland, of Holland Esquire fame.

Named after a song Paul Weller wrote for The Jam, which was recently reprised by Mark Ronson ("I've got a pocket full of pretty green, I'm gonna put it in the fruit machine…") and initially released in June, it comprises casual menswear pieces including hats, T-shirts and scarves. The premium line, which includes more classic, grown-up designs in silk and cashmere is released at the end of this month and will be stocked in Cruise in Edinburgh and Glasgow.

It's difficult to know how to approach an interview with Liam Gallagher. The 37-year-old father of three (he is married to All Saints singer Nicole Appleton) is one of those people whom it's difficult to imagine in real life. His public image is so cartoonish that it seems impossible that he maintains it when he's having a pint down his local.

His own brother describes him thus: "He's rude, arrogant, intimidating and lazy. He's the angriest man you'll ever meet. He's like a man with a fork in a world of soup." Still, I rationalise, there's only so much rock star behaviour you can get away with when you're promoting a clothing line.

I needn't have worried. Sitting across from me in a dimly-lit corner of The Garden Gate pub, Liam doesn't smile. A hint of a smile doesn't pass his lips once over the course over the interview, yet he is friendly, polite, accommodating, even warm. He jokes, he asks me questions, but is always unsmiling, to the extent that I find myself wondering if he's ever smiled. He's a serious man, but there are no hints of the petulant child his brother has described, or of the lairy troublemaker he has been portrayed as in the media.

"Obviously I've got kids and you know, just took me foot off the gas a little bit," he says by way of an explanation. "I've definitely chilled out. A lot of people sort of get scared…" he switches into mock hard man mode, jutting out his chin and mumbling as if he's picking a fight, before waving a hand dismissively. "I've definitely changed, I think for the better."

He is handsome in person, shorter than he seems on stage, and looks relaxed, fit and healthy. These days, he gets up at the crack of dawn to go for a run around Hampstead Heath. He does the school run every day. And, perhaps most shocking of all, today he is sipping mineral water. He is sharply dressed in a Pretty Green parka and jeans, his hair is cropped. He looks stylish, if a little stuck in 1995. But then the younger Gallagher brother has always been obsessed with clothes.

"It's just as important as the music for me. Yeah man," he says, taking a gulp of water. "You can write a decent tune, but if you look like a d***, that doesn't cut it with me, you know what I mean? There's plenty of bands I've heard and I've gone, 'F**king hell if they look good man, if they look cool then we're over.' Then you see them on the TV and go, 'Thank f**k; they look s**t.' If you look good and you've got the tunes then you're away man."

Critics of Oasis have observed that the band has stuck resolutely to a musical style – one heavily influenced by the past and by artists such as The Stone Roses, Paul Weller and The Beatles – refusing to change or to move with the times.

Critics of the clothing line might say the same thing. Much like his approach to music, Liam clearly knows what he likes and likes what he knows.

Where 15 years ago, young men copied Oasis in bucket hats, parkas and Clarks wallaby shoes, today they want skinny jeans, skinny shirts, skinny ties and pointy shoes, an aesthetic which Gallagher describes as "a disease" and refuses to pander to, preferring to channel the mid-90s – with parkas and bucket hats.

However Pretty Green has been selling well, with some pieces (the parka included) selling out almost instantly. Its website crashed seconds after it was launched, such was the interest from fans, and the premium line has been well-received by buyers. Martin Lacey, the buying director at Cruise describes it as "a fantastic first collection surpassing all levels of expectation".

"Pretty Green brings a whole new look to the market that could match any mainline brand for quality, attention to detail and design," he says. "Unlike previous celebrity collaborations, it can stand the test of time and stand up in its own right."

Certainly Gallagher is an unlikely figure in the fashion world. He has been to a fashion show once before, he tells me, with his ex-wife Patsy Kensit, "and I nearly threw up. It's not my thing. Sipping champagne and talking s**te? They're only clothes aren't they, really, at the end of the day."

He's a showman. He holds court physically, gesticulating, shuffling around in his seat and occasionally leaping up to emphasise a point. When I remark upon the ponyskin shoes he's wearing today, he jumps to his feet, planting one foot on the low table and flinging his arms out in a pose that seems to ask me to come and have a go if I think I'm 'ard enough, not, as is the case, to admire his cheetah-print loafers more closely.

"These are Yves Saint Laurent," he says proudly, pronouncing every consonant, "and these are the nuts. You want to see the reaction when I take the kids to school in these. They're just like, 'Woah your dad's got Flintstones shoes on!'"

I ask him about Scotland, where Oasis were first signed back in 1993 after Creation Records co-owner Alan McGee saw them perform at King Tut's Wah Wah Hut in Glasgow. "Scotland's f**king cool man I love it," he says, leaning forward in his seat. "The crowds up there are top. People are always cool and you know how to drink. You don't know how to drink as much as me but… nice people. I don't know about the Mars Bar thing, though." He shakes his head ominously at the thought of tackling a deep-fried Mars Bar, before gesturing at his manager who's sitting at a nearby table eating chips.

"What did we try up there Steve, with cheese? What the f**k was it? It was like f**king loads of mad s**t, chips and gravy with cheese on it wannit?" Steve shrugs, his mouth full of chips and Liam looks at me incredulously, as if asking me to account for my country's bizarre dietary habits.

He leans back repeatedly, knocking his head on a fringed lampshade behind him. He sits with his knees as far apart as possible and swats distractedly at a fly. I ask him about fame. He has been one of the most recognisable faces in British music for his whole adult life, after all. His eyebrows furrow.

"Fame means nothing to me. It means that people have seen you on TV or whatever. I'm in a…" at this point he pauses and abruptly corrects himself; "I was in a band who made music and that was it. Fame is just a f**king disease."

To be continued . . .