"They don't have a rude look about them. It's not like making a big pink dildo or the wanking arm," she says, gesturing towards a giant mechanical arm that is making an unmistakably masturbatory gesture on the other side of the gallery. From where we are standing it's hidden behind a wall of images which, on our side, feature cars in underground car parks and, on the other, feature a man (the artist Gary Hume, if you must know, one of Lucas's former boyfriends; "poor Gary") naked but for some vegetable genitalia. Some very excited vegetable genitalia.
"It does have a really ancient history, when you think about it," Lucas continues. "It's really weird what our culture is like. You only really get insights when you come up against it."
Well, Sarah, I say, looking at the well-endowed sculpture rearing in front of us, it's a design classic. "Yeah," she replies, cackling with laughter, "it is."
It's probably too late to issue a public health warning, isn't it? Too late to say this article contains copious mentions of "knobs", "wanking", "shagging" and "tits". Too late to remind you that Sarah Lucas, the now middle-aged Young British Artist, has always couched her feminist critiques in blokey humour. Too late to say this is an exhibition that contains a neon coffin, a vandalised car, minimalist furniture (that, yes, you're allowed to sit on) and a portrait of a young woman as attitudinal artist; an exhibition that, in short, takes in death, loss, art history and personal image. Because, let's be honest, you might not notice those things for all the knobs and wanking arms (my favourite is attached to a Zeppelin blimp).
Lucas has long been hailed as the wildest and bawdiest of the Sensation generation artists - no small claim among a group whose first principle was so often to shock. Dressed down in big boots, T-shirt and leather jacket, Lucas made her name with works such as Two Fried Eggs And A Kebab, her rude, funny, provocative visions of the female body (which was, of course, also a rude, funny, provocative vision of the male vision of the female body).
She still does that stuff. The last thing she made, she tells me, consisted of a pair of tights on a hanger "with a pair of stuffed tight tits attached to it". But some things have changed. She's older, of course, and so is the work. This survey of the last 20 years of her output - her first solo show in Scotland - is now taking place in a very different cultural moment. Not necessarily a better one, she says, as we stand in her Smoking Room, a shed wallpapered in the most lurid pages of the Daily Sport. "I didn't realise it was going to go this far into puritanism," she says.
And yet, she also points out, we are bombarded by sexualised images more even than in the mid-1990s when the New Lad was making his appearance.
"We live in times that are very puritanical in one way and extremely lewd on the other. Even the interest in paedophilia is puritanical and moralistic, and on the other hand it is a lewd interest in the way it's dealt with in the media."
There's another change in evidence here in the Smoking Room actually. "It smells a bit clean," she points out. "It smells like everything does these days. A lot of smoking has actually been done in here." She thinks she might have to do some at the opening.
Lucas is a little older these days, a little more lined and today a little rundown. She's no longer a YBA, more a MABA (middle-aged British artist), one who knows that time is on the turn. "Time's going pretty quick by now. I know so many people who are looking death in the eye." And yet she remains totally recognisable as the tomboy artist, fag in hand, gag to hand, who was the critic's favourite back at the height of Britart.
We look at a wall of her portraits. Does she still recognise the girl she was? "Well, I'm still in there somewhere, I suppose." She wonders if she could do a self-portrait now. If it would work. "It's one of those things about getting older, especially as an older woman. I probably thought I was being quite radical and not particularly girly and quite anti-fashion in that. But it's one thing to do it when you're younger, and different to do it when you're older, in the power it has for other people."
We are a culture that remains in thrall to youth, in other words - the thing that gave her such an impetus 20 years ago, of course.
Lucas grew up in London, a milkman's daughter. Contemporary art wasn't in the picture as a kid, but her dad was into DIY and her mum was interested in crafts. Making things was part of the pattern of life. Lucas liked the idea of being a writer initially, but ended up at Goldsmiths College and in the middle of a media storm as Damien Hirst, the Chapman Brothers, her mate Tracey Emin and others became the toast of the art world, fêted by critics, represented by Jay Jopling and bought up by Charles Saatchi.
Lucas is suspicious of the media myth of that time. "Of course a lot of up-and-coming artists think that if you get a show with Jay Jopling or something that's everybody's story, when in actual fact everybody's story even within that tight-knit group was completely different."
What she remembers is the frustration of others - blokes mostly - getting shows while she didn't. Maybe, for all the front, she wasn't as tough as she appeared to be.
At another point in our conversation she tells me "confident people used to really annoy me when I was younger". But Sarah, I say, you were surrounded by them. "Yeah … I didn't think it was honest. It used to really bug me. Now I think it's not worth getting on about it. It just escalates and doesn't help."
So are you telling me that Hirst and Emin's confidence back then was fake, that it was all a front? "Well, it's not for me to say. I think everybody has their doubts. Probably Tracey less than most people, actually."
Lucas is now in her fifties, can drive a car (a recent development) and has moved to Suffolk where she lives in Benjamin Britten's old house with her partner, Julian Simmons.
I wonder if her attitude to the body has changed over the years? She starts to talk about penises again. "Going back to this thing about blokes. I've always found the penis a really useful sculptural thing. I've always said, 'When in doubt … knob.' I used to try to make a knob out of any material." I'm laughing, but she's working towards an idea here - that her art is about the body, but not her body, or mine, or yours. "My body might change. Other people's bodies might change, but it's the notional body really."
Here is the thing though. Is that all we are, just bodies? Biological machines? Is there room for the soul in there. "I dunno. What do you think?" Well, yes, I tell her, I think I'm just meat and bone and evolutionary mechanism. "It's very tricky that. Obviously to some extent we're sort of machines, but then I wouldn't like to say …" She pauses, considers.
"It seems really fanciful to me to think that this is all there is. Why should this be all there is? What a peculiar thing. In an infinite universe, why the hell would this be all there is? It's not a matter of thinking what that 'else' might be."
We've travelled from sex to death to the infinite today. In the gallery, a giant arm rises and falls again and again and again.