Amy Winehouse really, really wants a bottle of vodka. It is mid-afternoon and she is sitting in her dressing room at ITV’s Sharon Osbourne Show, preparing to perform her comeback single, Rehab, a confessional number full of brass-band accompaniment and brassy lyrics all about how her drinking is not a cause for concern. Her band are around her, watching last night’s football match on telly.

Amy is pulling a brush through her immensely knotted hair, which is bunged up with hairspray and the general clog of a run of late, boozy nights. She has already given up on her stubbly legs and dirty fingernails. She repeatedly asks a producer to get her the vodka; finally he caves in and asks if she just wants a glass. “Are you having a laugh? Yeah, I just want a shot,” she deadpans. “No, I want a bottle,” she confirms, like a dipsomaniac Verucca Salt.

He leaves, returns having failed to find vodka, and is swiftly dispatched again. “In his head there’s probably two monkeys rubbing a stick together,” she mutters. Everybody laughs.

If it looks mean in print, it sounds funny when said aloud. Everything Amy says is funny, and she knows it. With her strong London accent and how’s-your-father repartee, she’s like a cockney barmaid, keeping the whole pub entertained with mockery and coquettish banter. She talks about the new anchor tattoo she has had done on her chest, “for sailors everywhere”.

She’s about to release a second album so good that it could win her a place in music history. Produced partly by Mark Ronson, New York’s hit-making producer du jour, Back to Black is full of belting tunes and often hilarious, but heartbreaking, lyrics, written by Winehouse. Her jazzy voice has developed into a turbo-charged, Etta James sounding smoky beast. Yet she looks more likely to win a place in tabloid history, her highly made-up face likely to grace the front page of The Sun lying in a gutter any day now. She has the drinking habits of a high-class tramp. Her favourite cocktail is a Rickstasy, which is three parts vodka, one part Southern Comfort, one part banana liqueur, and one part Baileys. Keen readers will note that this drink contains no mixer. “By the time you’ve had two of them you’re like, don’t even try and go anywhere. Sit down and stay down, until the birds start singing.” Have you had any bad times on this cocktail? “Oh no, never, I’m not a sick drunk. I’m a violent drunk.”

Well, that’s all right then. How violent? “Apparently, the other night at a gig, some girl came up to me afterwards and she goes ‘Hello’ and gave me a kiss on the cheek, and as she went away she goes to my boyfriend: ‘God she’s f***ed isn’t she’, and I just saw red and smacked her. I don’t remember this at all. Then I took my boyfriend home and started beating him up.” She laughs and laughs. “It’s not funny,” she adds, giggling more. Another night she hit a bloke in the pub who kept “punctuating his stories by slapping his hand on our table. It was just really really unfunny,” she cackles. “I have a really good time some nights, but then I push it over the edge and ruin my boyfriend’s night. I’m an ugly d***head drunk, I really am.”

Two years ago Winehouse released an album called Frank, emerging on to the pop scene at about the same time as Katie Melua and co. Winehouse was always far more interesting than them, with her belter of a voice, big jazz influences and larger-than-life personality to match. She was also larger than the skinny-minnies physically, but her womanly curves have all but disappeared. What happened to them? “I had a period where I struggled a little bit with eating disorders. Very, very recently. It was only a year . . . only a few . . . I only really stopped it . . .” She stops, then starts that train of thought again. “The thing is, if you’re an addict, you don’t get over it, you’re just in remission. So I won’t sit here and go, ‘Yeah, I don’t have a problem with food any more’. I do forget to eat a lot, and I do have my odd days where I think, ‘You can’t eat because you ate that yesterday’. But I think all modern girls are like that and I don’t like to make too big a thing about it.”

Winehouse’s new addiction is the gym. When not drinking, she manages to fit in a rather impressive two-hour workout several times a week. “I’m attached to the gym but that’s not a vice, that’s a good thing.”

In a not-knowing-what- she’s-doing sort of way, Amy knows exactly what she’s doing. She grew up in Southgate in North London, and now lives in Muswell Hill. She attended Sylvia Young stage school for a while, but only because normal school apparently couldn’t handle her. Her dad was a taxi driver, her parents weren’t particularly rich, and she ended up with her mum when they divorced, though she remains close to both of them.

Alex James from Blur used to say that you were all right being a drunk as long as you stayed in one night a week and rang your mum. I put this to her — she says she does do that, but that drinking is always involved in some way. “It’s too much of a drinking culture, everything tastes better with a drink. Like, watch TV: glass of wine. Cooking dinner: glass of champagne.”

Talking of which, her new favourite thing is oysters. “You just open them with a paring knife, bit of white wine vinegar, lemon and salt, and that’s it.”

So you even manage to get booze in your food? “No! White wine vinegar hasn’t got white wine in it. Has it?” She grew up listening to her dad’s jazz records and clearly knows her music inside out. When her manager enters the room asking her which cover version she would like to play at a forthcoming corporate gig for Russian bankers (“They love me, Russian bankers do. I dunno why cos they talk the whole way through my songs, but they love me.”), she instantly starts talking about Donny Hathaway songs. In fact, the late soul singer gets a mention in the Rehab lyrics.

“There’s nothing you can teach me that I can’t learn from Mr Hathaway.”

She also loves the Shangri-Las, and other old girl bands. “I like old Sixties heartbreak songs, girl-group comfort music, songs that you can sing into a bottle of whisky.” It is becoming clear that Amy’s drinking is not so much a symptom of depression as of a chronic case of nostalgia.

In these days, when it seems that pop stars such as Pete Doherty and Mike Skinner treat rehab like a five-star hotel to be returned to at leisure, Winehouse is making a statement about not wanting to go down that path, although rumour has it that her record label would like to see her sorting herself out a bit When, at her manager’s behest, she got as far as reception at a rehab clinic she soon realised that it wasn’t for her. When they asked why she drank so much, she explained that she was in love but that she was depressed at the thought of losing her boyfriend. She had “f***ed it up, and it was only a matter of time before he found out. Which it was.” They told her that her drinking was “ ‘symptomatic of the depression’. I said ‘ That’s correct.’ And the man said: ‘Well I’m an alcoholic and I’ve been this way for 50 years’ — which is tragic isn’t it? Horrible. I don’t ever want to be one of those people who can’t be around drink. And I’m not the kind of person who sees someone do a shot and goes, ‘I can do that! I can do three!’ I’m not like that. I can drink a lot and have a good time and not be absolutely twatted though.

Where’s my vodka?” Somebody has moved the vodka. An obliging band member returns it. “So yeah, he asked me to fill in this form. It was a psychological thing — how much do you drink, that kind of thing — and I said, how long’s it gonna take? He said half an hour, so I said no. Sweetpea, can I have a glass?”