"Howson, 55, has Asperger's syndrome and has suffered with depression and addiction for much of his life. I met him at Flowers Gallery in London to talk about his latest exhibition, his artistic heroes and his battle with mental illness.

It was the first day of his most recent exhibition, A Life, and as we walked through the collection of works - spanning much of his career from the 1980s to the present day - he said he was tired, but seemed happy, content even. He had been unwell a few weeks before, but was looking forward to spending the weekend in Glasgow with his daughter, who, like him, has Asperger's - a form of autism.

I was keen to ask about one painting in particular, The First Step, arguably one of the most striking in the exhibition. A hunched man, lined, scarred and bent double, carries an animated band of figures on his back through a gloomy landscape of broken glass. One of his unruly passengers goads him on by tearing his thigh with a giant hook. At the front of this group is a young blond girl. "That's my daughter," Howson tells me. "My daughter is almost always in my work. I think she's always kind of leading me, pointing to where I should go. It's autobiographical. I suppose it's a bit melodramatic, but that's the way I feel."

While working on The First Step in 2000, the artist was battling with addiction: "I was drinking a lot and taking a lot of drugs at that point. I'd been 25 years on drugs and drink, so that was when I first got better really, I suppose, and I had this incredible spiritual experience in the hospital. I stopped drinking and stopped drug-taking, got myself better and was really happy for a few years - three years I think it was - and then I just suddenly went downhill again. So it's been up and down all the time; being ill, being well, being hyper, being depressed. I can't seem to get this level track really."

The following are edited excerpts from our conversation.

Emily Spicer: The exhibition is called A Life. Is it autobiographical?

Peter Howson: All my work is semi-autobiographical. But the reason we decided to do it as a mini-retrospective is that I was too ill to do all the work for it. I've only just got better after being ill for six years.

ES: When you look at this exhibition, do you feel as if you are looking back on your life?

PH: Yeah, a wee bit, it's strange. I haven't seen these paintings in a long time. It's good to see them again, I suppose.

ES: You have been described as the Scottish Hieronymus Bosch. Is that a fair comparison?

PH: [Laughs] I'd like to be the Scottish Bosch, but I don't know if I'm good enough. But I will get better. I'm hypercritical. I think I've always suffered from low self-esteem, so I find it constantly amazing that people like the work.

ES: You were awarded an OBE in 2009, so that's an indication that you must be well respected.

PH: Well, maybe. I don't even remember collecting my OBE. I think I've been so ill that I haven't remembered it. I've had so many blackouts.

ES: So periods of your life are completely blank?

PH: A lot of it, yeah. In the past six years, I've really only remembered a few things. I don't even remember doing entire exhibitions.

ES: You've always been interested in conflict and battles and the darker side of things.

PH: I think it's just the way I'm drawn to things like that, drawn to danger. I don't know, it's weird; I can't really explain it. Ever since I was four I've been doing battle scenes and, even though Bosnia was hellish, I really enjoyed it, that's the weird thing. I really enjoyed being there.

ES: Did Bosnia change your view of conflict? Did you have a slightly glamorised idea of what war was like?

PH: No, I didn't have any illusions as to what war was like because I'd lived such a violent life before that. Obviously, I hadn't experienced real warfare before. Bosnia was definitely a shock, but I wouldn't have missed it for the world. But I suppose it had a knock-on effect.

ES: I've read that some of your paintings of Bosnia weren't hung in the Imperial War Museum. It wouldn't show them to the public.

PH: Well, there's one particular one it wouldn't show - the rape painting. I don't know. There was a big controversy, a big hoo-ha about it. It seemed like a storm in a teacup to me. It did show it in the end. I think it was the fact that it was advised to buy it and didn't. But David Bowie bought it anyway so it became quite a famous painting.

ES: Did you think the museum's caution towards it was a rejection of what you had seen out there, that it didn't want to show the sinister side of what was happening?

PH: I think what a lot of people had expected was a certain kind of thing in Bosnia - drawing and painting the soldiers, and I didn't want to do that. I wanted to paint the really gory, really tough stuff. That's what Bosnia was all about. It was a really violent war, mainly to do with ethnic stuff. At one point we went to rescue 150 rape victims and that day was the first day of my life in Bosnia where I didn't have any fear. I just wanted to get these women out of the territory and to safety, so I suppose that's when I started working really well over there. I stopped even thinking about art.

ES: Has painting helped you through the darker times, or is art a source of anxiety in itself?

PH: It's therapeutic. It's what I like best. I love being in the studio. I love working. It's a new experience for me to get back into it. I haven't been in the studio working hard for a long, long time. I've been kneeling on a hospital floor drawing, with the nurses telling me to go back to bed. I was heavily drugged as well. They drugged me up in hospital, so it was one thing after another. I just couldn't function.

ES: I notice there are a couple of paintings in this exhibition, done this year, that seem different; there's a change in your work. I'm thinking especially of The Bear.

PH: Well the boxer is just an old subject. They call me the bear because I'm strong and I'm bad.

ES: Looking at that painting, it seems that, although the boxer appears tough, there's a kindness in his eyes. Even though he has just taken a swing, there is a gentleness about the face.

PH: Well, it's kind of the way I feel, maybe. I'm getting my strength back now. I can feel my strength coming back. I used to be really fit. I used to run lots of marathons and be very fit and then I started the drugs and the drink and all that, and then I started getting really unfit, but this is me back again. I feel like the bear again. I feel strong again.

ES: And it seems to be a hopeful picture. The sky is blue and there's a tinge of sunlight in the clouds. It's uplifting.

PH: It's OK. I really can't stand the painting myself, but everyone else seems to like it. [Laughs.] I find it embarrassing. It's OK, people like it. I want to get better and better and better, and just really work away. The one I like is Alpha & Omega. I don't know if many people like that, but I like it, you see. That's the stuff I want to do.

ES: Can I ask what the title means?

PH: Well, when Jesus appeared to St John the divine on Patmos, he said: "I am the alpha and the omega; the first and the last." He said, write down what I'm going to tell you now, and that was the Book of Revelation. Jesus appeared resurrected, but it frightened John so much he just about died. He fell on his face, but he wrote down the book. He wrote it all down and it means a lot to me for my faith. I'm obsessed by the face of Jesus and the resurrection.

ES: Did you feel like John when religion came back into your life? Did you feel frightened at first?

PH: I've never been frightened about that, about things like that. I had the same experience when I was in hospital the first time because I was just about to commit suicide and they left me for half an hour - I was on suicide watch in 2000 - and suddenly something came into my room and a voice said: "Peter, this isn't the time for you to die, so get up." So that stayed with me for three months. It completely changed my life. The whole room filled with light. I never saw anyone: it wasn't like an angel appeared, it was just light, pure light and love, incredible love. Then it goes and you've got this struggle again. Christianity really is the religion of death anyway, so I've always had that thing about death. I suppose it's quite morbid sometimes, but it's also a joy as well because all I want to do is help people.

ES: I'd like to talk about the way you work because a lot of your paintings are based in the imagination rather than the observational. Where do the images come from and how do you put them down on the canvas?

PH: Just my head really. I studied anatomy for a long, long time, since I was four years old. And I did life drawing when I was very young as well. I drew my family. I was totally and utterly a recluse, even from a young age. I didn't go out anywhere; I just drew all the time and then decided I was going to use my imagination, so that's what I do. It just comes into my head. I visualise things, then I don't have to use models, and I seem to have this thing about anatomy where I can remember it, and I can remember any sort of pose, so I can do it from my mind and I love doing it. I love perspective, foreshortening, the distortion of the figure, you know, the limbs and the legs.

ES: So you don't need someone in front of you to do that?

PH: No, I never use people. I do every now and then use a life model if I need to practise something, but not very often. I don't really enjoy it. I just enjoy using my imagination. I suppose my hero is William Blake because he really hated academic art. He wanted to use the imagination totally and that's what I want to do. The thing is, he could only do small things and I can do great big canvases and I love doing them. I love cramming figures into them and I love the whole figure and the human face. To me, there's nothing ugly in the physical world; it's always spiritual things that are ugly for me. So the ugliest person for me would be beautiful. I love beauty, but I also see beauty in ugliness, even in the most tragic of places, of situations. You can get physical beauty, even in the worst of things, but not spiritual beauty. So obviously the rape scene is a terrible subject, but the actual painting - and this is the weird thing about art - can turn something horrible into something powerful and moving, and it changes people's lives and there is a kind of beauty about it as well. So rape is not beauty, it's evil, but the actual painting itself moves someone to want to buy it and there is a kind of beauty in the paint and the way it's used. It's very strange; it's almost like an irony, a kind of terrible, awful beauty about things. Look at the subject matter of Bosch - they're awful subjects of hell and yet they're beautiful. To me, they look beautiful.

ES: Is it true that you're not a fan of Lucian Freud?

PH: No, I'm not really, no. Definitely not. I don't know why, probably because it's just academic for me, it's just people and it's not really imagination. It's very cold and unemotional and slightly falsely bohemian and all that kind of stuff. You're not a relation of Freud, are you?

ES: No.

PH: Thank goodness for that. I find him quite an interesting person. But he couldn't paint anything he didn't see. I suppose my whole philosophy is based on the Trinity theory, which relates to everything in life. For painting, it's like three circles and in the middle is the main part. The first circle is God, which is the idea; the second circle is Jesus Christ, which is the technique; and the third circle is the Holy Spirit, which is the message. You have to balance out these things in your painting, so unless they're all balanced, you don't get a good painting. So you can actually tell what's a good painting and what's not. It's not to do with whether or not you like it: you might like it, you might not. I like a lot of bad art as well, but I know that if it's not good, it's not good. I don't like conceptual art because you can't tell whether it's good or bad. That's what I try to get into my painting. I try to get the idea, and the technique has to be great, and the composition and everything, and the message. You have to convey the message. If a painting or a piece of work doesn't convey an instant message, or even a hidden message that comes out at some point, it doesn't mean anything. So any art that has to be explained in a big write-up fails for me. It's the same for books, literature, poetry, the lot: if you're too obscure, it doesn't work, and if your idea is not good enough, it won't work. If you have an idea, but not the technique, it won't work. So you have to hold this balance of stuff. Freud had a brilliant technique but no ideas, and he just had to paint what he saw. Blake had all of these things because he could draw, he could paint; he could do the most amazing things. Michelangelo, had brilliant technique, brilliant ideas, brilliant messages.

ES: Your work reminds me slightly of Michelangelo's, with the writhing bodies and your use of mannerism in your figures.

PH: It is like that, definitely. Michelangelo had a real problem painting women. His women are all muscular.

ES: They have ice-cream scoops for breasts.

PH: [Laughs] Exactly, yes! He was an incredible character, I have to admit, but I think I've got to know him anyway. I know exactly what was going on in his mind and I know the spiritual battle he had as well. I know that there was crisis in his later life. He knew that art was not everything and that he'd done something terrible - we don't exactly know what that was - but he had this real crisis. His last pieces are his greatest, probably the last sculptures; they're quite Rodin-esque and Rodin must have got a huge amount from them. I love Rodin as well.

ES: And The Last Judgment - Michelangelo put his own image in that - do you find you do that as well with your work?

PH: Lots of times, yeah, I suppose I'm quite egocentric, I like to put my own image in it. What I love about The Last Judgment is - it's just incredible - the composition is beautiful and Jesus is raising his arm - it doesn't look like Jesus, but he's raising his arm - and he's just about to go like that [sweeps arm down] and decide the judgment, so it's an incredible painting. It's not what I believe in. I don't believe that people get sent to hell anyway. I'm not a religious maniac that believes some people are saved and some people burn in hell and all that kind of rubbish. I don't believe that at all. I think everyone gets in, eventually.

ES: It strikes me that you must be an incredibly resilient person to have come so far, given the challenges you have faced.

PH: I'm a survivor, I suppose. I had nothing at all in 1984, nothing. I didn't have a penny. I was homeless for a year in Glasgow - I lived on the streets - and then suddenly I met this woman and she took me home and said: "Look, why don't you just start drawing again." So I started drawing and about a year later everything changed, the whole thing blew up and it was all about money coming in and fame and whatever, and then it all went wrong again. Theoretically, I shouldn't be here because I've nearly died so many times, either with overdoses or with fights or violence or whatever, but I'm still here. There must be a reason for it."

Peter Howson, A Life, is at Flowers Gallery, Cork Street, London, until 11 January 2014.

Emily Spicer

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