Jimmy Somerville is reminiscing about his disco youth in Glasgow.

“There was this pub called The Waterloo,” he says of Scotland's oldest gay bar. “I won 10 pounds in there for dancing to Born To Be Alive by Patrick Hernandez,” he laughs. “And there was a club called Shadows, down at St George's Cross. I remember the first time I went there. I was under age, and it was secret and clandestine, so there was this slight atmosphere of fear. But I remember just thinking – 'Oh, this makes sense'”.

Disco has always fired up Jimmy Somerville. It's in the glittering protest-pop of his first band Bronski Beat (the hi-NRG electro of Why, the Giorgio Moroder-evoking alien(ated) disco of Smalltown Boy), it's in the soul-fuelled socialism – and activism – of the anthems by his second band The Communards (the dancefloor shimmer of their version of Don't Leave Me This Way, their cover of Gloria Gaynor's Never Can Say Goodbye), and it's all over his joyous solo back-catalogue, from his 1989 take on Sylvester's You Make Me Feel (Mighty Real) to this year's impressive album of disco originals, Homage.

“Yeah, disco's always run through me,” he nods. “I remember Shuffles on Sauchiehall Street was the first kind of grown-up club I went to. I was young but I managed to get in, basically because I looked like a little girl. I discovered a basement, and as I went downstairs, and they were playing Donna Summer's A Love Trilogy. I danced for 17 minutes. I remember the freedom, the feeling of safety. I was in my own world on the dancefloor, and that was it for me.” (Bronski Beat would go on to cover Donna Summer's classic I Feel Love with Marc Almond).

If Somerville's songs have always celebrated disco's sense of euphoria (albeit often shot through with melancholy), then so too have they long embraced its spirit of political revolution – of music as conduit for social change – from Bronski Beat's headlining 1984's Pits and Perverts benefit concert, to The Communards' anti-Thatcherite anthem, Breadline Britain, taken from the duo's chart-topping debut album, whose lyrics ring horribly true today (“People getting hungry and people getting poor / people getting destitute and more”).

“We treat disco quite dismissively now – it's all flares and big fizzy wigs – but it's more than that, and it's hugely political” says Somerville. “It's a genre of music that people on the fringes of society were listening to, people who took themselves underground, into basements, behind closed doors, to congregate and celebrate. As a teenager, I'd be on the dancefloor, knowing every lyric, singing along and twirling, because it was almost as though life outside wasn't prepared to allow me to have the freedoms that everyone took for granted,” he recalls of his experience as a young gay man in 1970s Glasgow.

Many of the criticisms of disco were nothing to do with the music, of course: they were rooted in homophobia, or racism, or both. “Exactly,” he says. “The big one for that was the Disco Sucks campaign – when white, conservative, republican, red-neck America were burning disco records. That wasn't about music, that was about people they thought had no right to be visible or have a voice. The politics of that were massive.

"Disco became a space where people congregated,” he continues. “And when you get people together, the therapeutic benefit of realising you're not alone is huge. The whole momentum of what disco did for gays and for black people was just incredible.”

If Somerville's music and politics always had disco as their true north, then so too, it seemed, did his singing voice – an impeccable, clear-as-a-bell falsetto. Did he find his voice through disco too?

“Oh no, that wasn't until much much later when I'd moved to London, in my early 20s” he says. “That was all by accident. I mean, I'd been singing along with female vocalists and disco records all my life, but I had no idea I was going to do something with it – I didn't want to be a singer, or be in a band. I did it more because of politics and understanding that, you know – 'Oh, I've got a platform here! People are taking an interest!” And also because a part of me was like, 'Oh, and I'm getting attention!'” he says with a laugh.

Did he always feel a sense of responsibility to address social and political issues through that platform?

“Yeah, I did,” he nods. “When people say, 'Oh there's no room for politics in music', I think that's a lot of s***. And I felt even more strongly about that when I was a very angry young man. My politics at the time had been driven by a really quite radical, left-wing socialist, Trotskyist ideal, so I just threw that all together, set it on fire, and hoped for the best.”

If his music was provocative, so too were his interviews. The Communards in particular astutely exploited the pop music media as a tool for discussing sexual politics and raising social awareness.

“Absolutely,” Somerville nods. “Richard [Coles, his Communards bandmate] and I were in touch recently, and I was saying to him, we should always be proud of what we achieved. We were one of the first few people to go into a magazine like Smash Hits and talk about homophobia, discrimination, Aids..”

Somerville's coming of age as a gay man in the early – fearful, unknown – days of the Aids epidemic had a huge impact on his art.

“I'm still very connected to a lot of those songs because of that,” he says. “For A Friend is about one of the first closest friends I had who died from an Aids-related illness. I was 26, he was 26, and at that point I was going to New York a lot and I fell madly in love, and I was going there a lot, and having relationships, and dealing with all these people dying or disappearing. So a lot of the songs were fired up by the situations I was finding myself in.”

He continues: “And the opening lyrics to Why – 'Contempt in your eyes / As I turn to kiss his lips' – you know, as progressive as we are even now, there are still people who'll be waiting for someone to turn a corner, to whack them over the head, because they saw them kissing another man.”

Somerville's disco anthems remains as socially and politically resonant as ever, but the most powerful, and haunting, remains Smalltown Boy, which closely echoes the singer's own (need for) escape from Glasgow to London as a young man.

“Smalltown Boy's a real emotional cry from the heart,” he says. “It's about this idea that we all crave something, we all want to discover who we are, and what we are. And whatever journeys we take, we hopefully find out – eventually – what that is.”

Somerville's own journey will bring him back to Scotland this weekend for Rewind. But for all the festival's retro kicks, it feels like Somerville is looking forward – Homage is his most positive, and convincing, album in years. It's political too, of course, not least on recent single Travesty, with its rallying cry about welfare war.

“But it finishes on this idea of hope,” he adds, shining light on his dark but glittering songs. “As long as I breathe, I hope. I'm a very optimistic person.”

Rewind is at Scone Palace, Perth this weekend.