'EURGH, I FEEL so uncomfortable!" complains Shirley Manson, squirming around on the minimalist sofa of the Harvey Nichols personal shopping suite, where the Scotsman's photographer has arranged her into what is, it has to be said, a fairly innocuous pose.
She leans forward, contorting her angular frame towards the camera and narrowing those luminous blue, kohl-rimmed eyes, but awkwardness is etched all over her face. The photographer tries a different tack, placing a flash gun to her right. "Side lighting? For a woman?" enquires Manson, raising an eyebrow. She looks over the photographer's shoulder and gives me a wink and I wonder, not for the last time during our encounter, whether she's being difficult on purpose.
After all, Manson's reputation does tend to precede her. As the gorgeous and surly frontwoman of Garbage, an American band with a huge following on both sides of the Atlantic, the Edinburgh native achieved worldwide success during the 1990s with hits such as Stupid Girl, I'm Only Happy When It Rains and Push It. She cultivated a spiky, don't-mess-with-me attitude that was only enhanced by her flame-red hair and outrageous statements, like the time she told a journalist she'd bought an orange Fender Stratocaster because it matched her pubic hair.
As soon as the photographer leaves the room, though, Manson starts to mellow. She admires my shoes and emits a sudden crackle of laughter when I tell her how much they cost (not a lot). We talk about Waverley Care, the Edinburgh Aids and HIV charity of which she is a patron of and to whom she has just presented a cheque for 51,000 on Harvey Nichols' shopfloor. This she has done on behalf of the MAC Aids Fund, for whom Manson was once a VIVA GLAM ambassador (promoting the range of MAC lipsticks whose proceeds go to support Aids projects).
"It's not a pretty charity and it's not a pretty disease," she says. "People are uncomfortable talking about it and, as a result, it's been swept under the carpet to a certain degree. There's a terrible stigma attached to it.
"I remember the huge furore about HIV and Aids in the early 1990s, and being really frightened. There was a fearful feeling about having unprotected sex. But young people now seem to be pretty lax about taking care of themselves."
Manson herself lives in Los Angeles these days, though she still has a house in Edinburgh. She says she's done with Garbage, for the moment at least. "I just got to the point where I couldn't sing Stupid Girl any more," she says wryly. "I'm far too smart for that."
For years now, rumours of a Manson solo album have hung in the air. An interesting slew of names has been connected with the project – everyone from Jack White of the White Stripes to Paul Buchanan of the Blue Nile, Billy Corgan of Smashing Pumpkins and solo singer Beck. But whether some, all or none of these have been involved (Manson, in one of her more stubborn moments, refuses to elaborate), the project has hit the rocks.
"I had a lot of material, but unfortunately I played it for my record label and they thought it was very 'noir', which I took as a huge compliment until I got home and realised they didn't mean it as a compliment at all. As a result we're sort of at an impasse. I don't know what will happen. I think, maybe, they have a different idea of the kind of career I should have to the one that I want."
So what kind of career does she want?
"I'm 41," she says. "I'm a woman, I'm not a kid any more. I'm not interested in getting up in a short skirt and singing a pop song. Unfortunately, record labels feel that's what they need in order to have success. Look at Madonna. She's still having to churn out pop hits and she's 50. I don't think that's right.
"I've had a really successful career. I don't really need to do anything for money and I certainly have no intention of doing that. I just want to live a creative life and sing songs that have some meaning for me personally."
She says she remains very proud of the solo music she's written, and she's hopeful it'll see some sort of release in the future. But with the album on the back burner for the moment, she's been working on "a couple of collaborations" – she declines to reveal who with – and having a sort of middle-aged gap-year by going travelling.
"I wanted to go to all the places I never went with the band, because otherwise you just feel like you're working. I went to Laos, which was incredible, and to India and Bhutan. They're really off the beaten track and it was an incredible experience. Going to these sorts of places really changed my perspective. You go to the Third World and you see children living on a traffic island and it's shocking. Really sobering."
Perspective has always been a difficult thing for Manson. She has struggled with body dysmorphia – an emotional disorder where the sufferer is crippled by constantly feeling ill-at-ease with their physical appearance, regardless of what they actually look like – since her teens. Growing up in Stockbridge, where she was both a Brownie and a Girl Guide, she also went through a period of self-harming.
"I look at my mum, who is 72 and has never had a stitch done to her face, and to me she looks beautiful. So I just have to remember her when I'm struggling with the image that looks back at me from the bathroom mirror. I just want to learn to live with myself. Because sooner or later, you have to."
It is, I think, a poignant thing to hear from someone so beautiful, and particularly from someone who has spent the past 15 years in the showbiz spotlight all around the world. But then, as she demonstrated earlier, posing for photographs has never come naturally to her. She admits that the condition is still an issue for her.
"I think to a certain degree I'll always have it," she says with candour. "But I see it in all my girlfriends as well. I mean, even someone like Gwen Stefani (a close friend of Manson's – the two have even performed together], who is undoubtedly a beautiful girl, is completely unsure of herself sometimes. Every woman I know is judging herself really harshly against pictures in magazines. It's ludicrous, because all these girls are either 12 years old or they're being Photo-shopped, yet we're beating ourselves up to look like that."
Manson is divorced from Edinburgh sculptor Eddie Farrell, whom she married in 1996 and maintained a strained, transatlantic relationship with until their split in 2001: she is now seeing someone in Los Angeles. "He's over there," she says with a don't-ask-me-any-more-about-it laugh. "I keep him over there."
While she's seemingly settled with a partner, motherhood is off the agenda. It's an issue she's clearly wrestled with.
"I don't want children and I don't know why. I wish I didn't feel like that… for some reason I feel guilty that I don't want to be a mum. I feel a wee bit funny about it, but…" she hesitates, and I can see her mentally listing her reasons.
"No," she says finally. "I can't begin to tell you how many times I've been round at a girlfriend's house and they're in their sweatpants and they're miserable and haven't washed their hair in a week and they've got baby sick all over their boobs and they're saying 'when are you going to have a child? It's great', and later I leave their house thinking 'thank God that's not my life'.
"I understand it's an incredibly fulfilling and wonderful experience, but I feel like I'd just be so neurotic the whole time. I've just adopted a rescue dog and I found that really stressful. I think having a child would just be too much."
She seems to understand herself pretty well these days. The difficult rock chick who always looked like she'd steal your boyfriend and your favourite top is gone, replaced by a more serene, grown-up character. She might still borrow your favourite top, but she'd give it back eventually and she'd probably have washed it, too.
"Recently I've realised I'm a happy person, compared to the miserable person I used to be," she says, still looking surprised at the revelation. "I think age has helped, and obviously so has having a fulfilled career. I don't have that weird chip on my shoulder I used to have."
She produces another one of those surprising bursts of laughter and for a moment her whole face lights up. It's the expression the photographer was searching for all along.
• All proceeds from MAC Viva Glam products go to help people affected by HIV/Aids. Fur further information please visit the MAC counter at Harvey Nichols in Edinburgh.