Jonathan Heawood: The act of extreme desperation

For many political prisoners, languishing in the world's worst prisons, the body is their most effective means of communication with the outside world. Scarred not only by the marks of physical abuse but also by the results of their own protests, some prisoners send the ultimate message of defiance: they starve themselves to death.

A hunger strike by the Iranian film director, Jafar Panahi, has caused uproar in Cannes this week. Arrested on unspecified charges, Panahi has been imprisoned in Tehran's notorious Evin jail since March. Due to attend the Cannes film festival as a judge, his imprisonment and now hunger strike have outraged fellow film-makers. Abbas Kiorastami has said that when a film-maker is imprisoned "it is art as a whole that is attacked". Steven Spielberg has launched a petition; Juliette Binoche has sobbed.

Yet Panahi's hunger strike is only one of many currently taking place around the world. In Morocco, the journalist and environmental activist, Mohammed Attaoui, began starving himself on 29 March. In Azerbaijan, the journalist Eynulla Fatullayev staged a hunger strike in which he was joined by other prisoners and supporters outside. He ended the strike after 12 days – but two days later he was put in solitary confinement. In Cuba, the anti-government protester Orlando Zapata Tamayo sustained an 85-day hunger strike that led eventually to his death on 23 February.

Some are sceptical of these hunger strikers. According to the US National Lawyers Guild: "Cuban prison officials acted properly when Zapata decided to go on a hunger strike". This trust in a prison system that even the International Red Cross has been refused access to is bizarre. It suggests that hunger strikers are merely attention-seeking extroverts.

I have read countless testimonies of the nightmarish conditions in prisons from Azerbaijan to Zimbabwe, from Belarus to China but I didn't really grasp what they meant until, in November 2008, I saw at first hand how hundreds of political prisoners in the Maldives were detained in metal boxes, six to a cell, in the equatorial temperatures of Maafushi prison.

The newly-elected President, Mohamed Nasheed, had been imprisoned there himself as a dissident journalist in the 1990s. The day after his inauguration I accompanied his special envoy, on a tour of the jail. The inmates, frustrated that they would not be released immediately, began to riot. Naked in the tropical night, they hurled themselves against the metal walls of their cells. The noise was like nothing I've heard before or since: humanity reduced to its animal components – sound and fury, signifying only the will to be free.

We ignore the insides of the world's prisons at our peril. Labour preferred not to hear from prisoners, at home or abroad. The new government has an opportunity to put prisoners back at the heart of its human rights policy. British ministers and ambassadors should insist in all their representations on the need for independent access to prisons by the International Red Cross and other NGOs.

For prisons are not just places to put criminals. They also tell a profound story about wider social relations in their country. Brutal, impenetrable prisons are a powerful tool for states that wish to silence their people in the face of abuse and corruption. The more deadly quiet the prison, the louder its message: "abandon all hope of political change, you who risk entering here".

The outraged cineastes of the Croisette should remember that Jafar Panahi is only one of many hunger strikers around the world right now. We shouldn't turn our eyes away from their plight. But nor should we forget that they are merely the expressive tip of an iceberg that reaches deep into some of the world's darkest places.

Jonathan Heawood is the director of English PEN, the writers' organisation