Lukas Graham single '7 Years': A catchy song about growing up in a 'utopian community' in Denmark is a massive hit

Just when we thought we didn't have any more space in our life for 21st century Denmarkia, along comes another slice of Danish. This time, it's a singer: Lukas Graham.

The single by his eponymous band, “7 Years”, won't be released in the UK until March but it's already been a hit all around. Across Scandinavia, it's been a number one. In the Benelux region, it went top 10. It's pop hip-hop, with sighing strings and an almost overwrought, consciously tremulous vocal. It's the kind of song that gets crowds waving hands in the air, swaying and singing along.

In the US, he has made just one TV appearance, last year, on Conan. When the late-night show unveiled its end-of-year viewers' poll, the band's performance of “7 Years” got a scarcely believable 98.86 per cent share of the vote.

The track was produced by a Danish backroom team known as Future Animals (one of whom, of course, also owns a fashionable restaurant in Copenhagen). The lyrics are by the singer himself, under his full name, Lukas Graham Forchhammer – an indication of his cross-national heritage. It's a highly emotive song. The singer recalls his childhood, his hopes, his dreams – and smoking weed at 11. He looks forward to turning 60. It's personal. “I couldn't go any further than 60 because my father died at 61,” Graham, who is 27, has said.

It's already had more than five million YouTube hits with two official videos. One is a montage of family photos; the other was filmed partly in Los Angeles – where the singer was signed by Warner Bros in 2013 – and partly in Christiania, a part of Copenhagen where Graham was born and brought up and is perhaps the most intriguing aspect of the whole story.

A woody enclave by a lake, Christiania is just down the road from both four-time “world's best restaurant” Noma and the parliament building we know from Borgen. In, but not part of, Copenhagen, Christiania is the closest the modern world has to an autonomous village-size utopian community, a place where dogs run wild and dreamers – Graham's parents, for example – dream new ways of life. No guns, no cars, no fireworks; lots of street murals; and a house made entirely out of windows.

Its mission statement was written by Jacob Ludvigsen, one of its many founders. For him, it was “a self-governing society whereby each and every individual holds themselves responsible over the wellbeing of the entire community”. A sardonic US TV presenter called it a place “where people can just live free, man”.

It's been that way since 26 September 1971, when Ludvigsen helped to lead squatters into an abandoned military barracks that had been built on the city's 17th century ramparts. (It was also where, after the war, Denmark executed its Nazi collaborators.)

Christiania is a tiny place, with a tiny population. One count yielded 600 adults, 200 children, 200 cats, 200 dogs, 17 horses and two parrots. Of the adults, more than 150 have been there since the start. Actress Britta Lillesoe is one. “It was fantastic to be young and do what you wanted to,” she says.

The community has its own anthem, with the opening line “People get filled with shit about us”. It has a slogan: “Lev livet kunstnerisk! Kun dode fisk flyder med strommen” (Live life artistically! Only dead fish follow the current). And it has a flag: three yellow dots on a red background. It's said the dots represent the Os in “love love love”.

It also has what is perhaps the world's biggest open-air hash, weed and drug paraphernalia market, which is one of the main reasons that the district is one of Copenhagen's most visited tourist attractions. The market is in what the Christiania council calls the “green light district” – but everyone else knows as Pusher Street. There is a Woodstock pub. Blocks of hash resin, wrote one visitor, are “lined up like cheeses at a delicatessen”, along with baggies of buds and ready-rolled joints in plastic tubes.

The market had its ups and downs, sometimes tolerated by the authorities, sometimes subject to regular police patrols. There are “no photos” signs – not to shield the privacy of the town's dreamers, but to protect its dealers from surveillance. Tourists who take pictures will be chased. To film there, it's possible Graham had to make a deal with the dealers.

Over the years, there have been days of riots, a machine-gunning (one death) and a grenade attack. In one crackdown, the police dismantled all the drug stalls. One, Snyder ryg med hjem (Snyder's Smoke Takeaway), was preserved, however, and reassembled in the Danish National Museum, such are Denmark's contradictions.

Drugs are big business in Christiania. Ten years ago, each dealer was estimated to be earning €325 (£246) an hour. Both the government and independent academics give an annual figure of $170m, which would give Christiana a GDP per capita of about $2m.

But the drug money doesn't stay in town. As everywhere, the trade is controlled by criminals – in Christiania, by biker gangs. They don't live in the area, but do cause serious parking problems in the surrounding streets and have physically attacked traffic wardens trying to issue tickets.

The area's free spirits and its dealers live in uneasy truce. In the past, hard drugs have been forced out by the residents. For now, though, they just don't want to talk about the biker dealers. Silence is safest.

But that kind of money is perhaps what the anarchists of Christiania need more than anything else right now. As with all modern city stories, whether idealistic or hard-nosed, this one ends up in the estate agent's window. With its location, Christiania is a super-prime piece of property.

A few years ago, a deal was struck with the authorities whereby Christiania's residents would buy the land for $12.5m (£8.75m) – way below market value. The deal was supported by a loan from those very authorities – with no set payback date. The idea was to sell shares to residents. They didn't seem that interested, as might be expected of the anarchically inclined. Little more than $1m has been raised.

Traditionally, a pop star would celebrate newfound success by buying their mum a house. When “7 Days” has made its millions , perhaps Lukas Graham could go one better and buy his mother shares in her whole home town.