In Eastern Europe during the decades before communism fell, samizdat literature possessed a raw, pent-up energy precisely because officially it was not allowed to exist. Artists and writers were beating with their fists on their own prison walls. "Is something similar still happening in Cuba?" I ask myself as I walk around a beautifully displayed exhibition of work by six Cuban artists who live and work in Havana, some well-established, others just emerging, at the Institute of International Visual Arts (Iniva) in east London.
The theme is heavily, if not ponderously, socio-political. It is about negotiating your way through the difficulties of being a citizen of a country with an ossified economy and, in practice, two currencies - the US dollar and the Cuban peso. There is nothing else worth talking about but the social. Life on that small island, within breathing distance of Uncle Sam, and with a decrepit economy and crumbling health-care system (don't believe everything you saw in Michael Moore's Sicko), is too complicated and too difficult to be worthy of naked celebration. This doesn't mean that the show lacks humour. The Cubans still laugh a lot, thank goodness.
For all that, everything I look at in this exhibition represents a kind of protracted howl of protest about the predicament of an island people who still suffer an intolerable measure of unfreedom. That includes everything from Isla, Yoan Capote's painted diptych of a troubled sea whose waves are constructed out of viciously barbed fish hooks - as he describes the piece, the artist holds out his fingers to show just how much he bled as he was making it, staining his own sea - to Autocensura ("self-censorship"), a video by the youngest of the six artists, 27-year-old Jeanette Chávez, in which we watch her binding her own tongue with cord until it turns blue and then closing her mouth.
How much unfreedom do they really suffer these days? I ask the veteran Cuban co-curator of the exhibition, Gerardo Mosquera. After all, this week and next the artists are all here in London, being feted by the international press, introduced to curators, gallerists and Sotheby's. Some of them already show regularly abroad. In 2006, Yoan Capote won a coveted fellowship from the Guggenheim Foundation in New York. So, perhaps, these are not the blackest of black days.
"There is still a great deal of unfreedom in Cuba," Mosquera tells me over a cup of green tea in the cafe. "The press is not free. The media are not free. Even before perestroika, artists in Cuba adopted a critical stance. Their art was reflecting upon the failure and the collapse of the communist utopia. They were making art about what was happening in Cuban society."
All the same, aren't things much better now? Yes and no. "Well, there is some censorship, but it is of a fairly subtle kind these days. Artists are tolerated because the authorities feel that they are a minority: these intellectuals are simply not worth bothering about. On the other hand, all these artists have to apply for a permit to travel each time they leave the country. Every citizen has to do that.
"That is not right. No citizen should have to apply to leave their own country. It doesn't cost much - just 25 Cuban pesos - but it is a way of putting pressure on the artist. Big Daddy will either allow you to go to the party . . . or not."
The veteran participant in this show is ázaro Saavedra (born 1964), who belongs to a generation of artists that emerged in the 1980s. His peer group was a bunch of idealists, Saavedra tells me, who believed that art could change the world. Now, being a little older, he is not so naive. One of his most recent projects involves the online publication of a political cartoon. (Just 2 per cent of the Cuban population even has access to the internet.) Such a cartoon could never appear in the press.
I catch up with Saavedra in the doorway of the gallery. He is leaning against the door jamb, shrugged inside a heavy coat, looking troubled and impassioned for reasons best known to himself. I ask him about unfreedom. He responds, in Spanish, with speed and volubility.
"No, things are not as they were in the 1960s and 1970s. Artists are no longer blacklisted. You no longer get a phone call out of the blue. These days the censorship is more sophisticated: they will talk about space, or health and safety matters. There are very important human rights issues," he says. "It could be a destabilising act, for example, to distribute the Universal Declaration of Human Rights in the street."
He starts to climb the stairs, and I follow after him. He throws these words back over his shoulder: "I have some hope now - I have the email gallery, and that's good - but I am not the idealist I was back then. Artivism, not activism."
I wander around in the downstairs gallery a little longer. In the centre of the room, at head height, hang a couple of what look like upturned black, plastic waste bins a couple of metres away from each other. The piece, by Iván and Yoan Capote, is called Secreter. Stand under one of them, and invite a friend to stand under the other. It's just like one of those children's games: whispered, clandestine messages pass to and fro. Sometimes you hear things right. Sometimes what you hear may be a distortion of what was said - or perhaps even a rumour.
The work is about the difficulty of free and honest communication in Cuba. Like much of the art in this show, it is hard-hitting and direct. But one aspect of all this does trouble me somewhat. The piece is so beautifully made. It should be more decrepit than this, more at the bricolage end of things. There is something slightly inauthentic about such a polished show coming from a country in tatters: it all feels a bit too generalised, a bit too designer-chic. A lot of money thrown at a great deal of well-honed pain.
"States of Exchange: Artists from Cuba" is at Iniva, Rivington Place, London EC2, until 22 March. For more details, visit: www.iniva.org