There are plenty of extraordinary things to look at in the Spitalfields studio of Gilbert and George, but the first thing that catches the eye is the vast poster of David Cameron in pride of place on the back wall. It turns out contemporary art’s most famous double act are big fans.

“Cameron is lovely, and so is George Osborne,” says George earnestly. “George Osborne especially because he is very solid, honourable. I think he looks like a matinee idol, he’s glamorous.”

Gilbert chips in. “Yes, George Osborne is our favourite because he looks like a grown-up schoolboy.”

George breaks into a knowing smile. “I bet you won’t find a Cameron portrait in any of the other artists’ studios.”

Facebook Twitter Pinterest Gilbert and George with two banners from their White Cube gallery exhibition. Photograph: Christian Sinibaldi/The Guardian

Constantly defying expectation and the norm has formed the basis of Gilbert and George’s extraordinary partnership since 1967. And while their allegiance to the prime minister might seem surprising, neither of the pair, now 71 and 73, believe politicians have the vision to effect change. As they keenly point out, it is artists and poets who have led centuries of progress – politics has always followed reluctantly behind.

It is this idea that is at the heart of their latest exhibition, Banners, which opens at the White Cube gallery from 25 November. Abandoning images for pure text, the show is a series of spray-painted slogans on large white banners. “Gilbert and George say Fuck the Planet”; “Gilbert and George say Decriminalise Sex”; “Gilbert and George say Burn That Book”; “Gilbert and George say Ban Religion” are among the controversial messages scrawled in red and black across 30 massive sheets of paper, proving that their delight in offending the liberal, art-going masses has not waned.

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The messages appear deliberately provocative, but Gilbert and George suggest they are both honest and positive. Burn that Book, for instance, symbolises being liberated from the regimen of organised religion and schools, while Fuck the Planet is inspired by the writings of Prof James Lovelock, which Gilbert and George first read more than 20 years ago.

“We need to just leave nature alone,” says George. “Human beings should only be in the city because it makes them freer and more tolerant than the ones isolated on top of the mountain. Nature breeds intolerance and excessive love of nature always leads to totalitarianism. Love of soil is the worst.”

Gilbert nods, adding: “It’s the same as the love of God, who is just another dictator.”

The idea for the banners first came just over a year ago, when the pair were asked to take part in the annual Serpentine Marathon, a series of 24-hour artist talks and presentations held at the London gallery. The theme was extinction (“which seemed extraordinarily bleak to us”), and instead of making any kind of speech, they decided to write messages – namely “fuck the planet” and “burn that book” – and silently hold them aloft for four minutes.

This was never meant to turn into a series, but Jay Jopling, who runs the White Cube gallery, caught site of the discarded banners during a visit to the pair’s studio and “got very excited,” says Gilbert, “I think because they bring out the hooligan in him”.

Facebook Twitter Pinterest Gilbert and George outside their Scapegoating show at the White Cube gallery. Photograph: Linda Nylind/The Guardian

The “appalling messages” of Banners, says Gilbert and George, are not about violently attacking the viewer, as was the purpose of their Scapegoating series shown at White Cube last year, but about liberating audiences from liberal complacency.

“Europe is frigid,” says Gilbert. “People don’t know what to think and they are not able to say anything anymore because they are so liberal they are not allowed – they have lost their moral fibre, the moral strength, lost all their conviction to act.”

George adds: “Artists are all anti-Bush and anti-bombs and have this line of common thinking which is just unthinking prejudice. We say what they are too terrified to.”

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The Banners are a succinct expression of Gilbert and George’s vision of the future – a secular, sexually liberated world, freed from religion and political correctness.

“We are in advance of politics, we think,” says George. “It’s a very simple fact that the novels of Dickens preceded legislation that stopped children working in factories. You have to have the knowledge and the culture first and then the politicians are dragged into doing things and changing things. The force of culture is generally misunderstood.”

Gilbert and George artworks may sell for millions these days, but the pair’s desire to push the boundaries of offence (George: “Good taste is the death of modern life, it wrecks everything”) has always protected them from the corporate clutches of the art world.

“We have certain amount of unsellable art and that is the good part, because it keeps us alive and confrontational,” says Gilbert. “Art has just become decoration for the very, very rich. We manage to keep our feet on the ground. We have never been part of an elitist art group. Our art is so confrontational that a lot of collectors would never touch it because they don’t want a naked shit picture in their living room.”

They revel in the controversy but admit that having to constantly defend their art for 50 years can sometimes be exhausting. They would like to have more of their art hanging in public spaces, in the Tate for example, but say they can’t because of “prejudice”.

Facebook Twitter Pinterest Gilbert and George in their home in London. Photograph: Christian Sinibaldi/The Guardian

They also keep themselves in their east London bubble, living and working together in the three Spitalfields houses they own and eating at the same Dalston restaurant every night. They never use the internet, have not been to the cinema since 1979 and do not listen to music because “it’s against our religion – it’s too soothing. It enters the brain and takes over, doesn’t it, steals your head.” Even the gentrification of Spitalfields and east London does not concern them.

“We love it all,” says George. “We think all change is progress. We think it’s very good – we don’t get insulted by people anymore. The middle classes took the danger away.”

But while they celebrate many of the excesses of the modern world, even Gilbert and George say it can still be difficult to be heard among the clamour.

“More and more it is difficult to speak as an artist,” admits George. “Nobody hears you because there are too many and there are too many different ways of making art today that there didn’t use to be when we started out in 1969.”

“We have to shout louder with our pieces,” adds Gilbert. “Much louder now, all over the world.”