What bars! Cars! Cigars! What prisons!

What do you call a country that ruthlessly suppresses dissent, drastically curtails access to the internet, bangs up opponents for 20 years or more and executes convicted criminals by firing squad? The answer is plucky little Cuba, destination of choice for thousands of British tourists who love its bars and vaguely think they are supporting the country's heroic leader, Fidel Castro, against nasty US imperialists. Tell that to Marta Beatriz Roque, an economist serving 20 years in a Cuban jail, where she has lost 30lbs from vomiting and diarrhoea since April. Or to Manuel Vazquez Portal, a writer sentenced to 18 years, who managed to smuggle his diary out of prison in May. "Thank God my family brought milk, otherwise I would have died of hunger," he wrote.

Roque and Vazquez Portal are among 75 dissidents rounded up in March, including more than 40 co-ordinators of the Varela project, the main pro-democracy movement in Cuba. In April, they were sentenced to a total of 1,454 years in jail, an event that would have British MPs jumping up and down in outrage if it occurred in countries to which they do not have a long-standing sentimental attachment. Not only is that not happening, but MPs and ministers fly out with monotonous regularity to suck up to Castro at six-hour back-slapping dinners and praise his autocratic rule. So it is an enormous relief to see these double standards beginning to crumble: on Thursday, three former presidents of European countries published a powerful letter denouncing the "Cuban Stalinists" and calling on democratic countries to support dissidents, political prisoners and their families.

The letter was signed by Vaclav Havel of the Czech Republic, Arpad Goncz of Hungary and Lech Walesa of Poland, who unequivocally described Castro as a dictator. The same day, I happened to be at the Foreign Office, listening to the Foreign Secretary, Jack Straw, launch his annual report on human rights. It highlights the absence of opposition parties, an independent judiciary and free trade unions in Cuba, and is a must-read for some of the Government's own backbenchers. "State security subjects peaceful opponents of the regime to surveillance, detention, house arrest, bureaucratic harassment and loss of employment, housing and other benefits," it declares. The one-day trials of dissidents in March were conducted "in violation of internationally accepted human rights standards", while three Cubans who hijacked a ferry in Havana harbour in an attempt to escape to the US were tried, condemned, put up against a wall and shot in the space of six days.

Now it is perfectly true, before you ask, that I have not been to Havana. I chair the English PEN Writers in Prison Committee and unlike all those salsa-dancing tourists, I cannot get a visa. PEN has campaigned for years on behalf of imprisoned journalists, novelists and librarians on the island, and the regime does not welcome human-rights activists, UN special rapporteurs or even representatives of the Red Cross. But I know that the effects of the repression are dire, driving talented young people into the arms of the ghastly right-wing Cubans who congregate in Miami, waiting for the old tyrant to die. A country that has the natural and human resources to become one of the most prosperous in the Caribbean has been condemned to remain a crumbling backwater, even if it does have a very fine health service.

But as a former foreign secretary, Robin Cook, has argued in my hearing, human rights are not an optional extra, something governments should get round to once they have achieved vaccination targets, but an essential feature of civil society. The great untold story of the 20th century is the remarkable increase in the number of democracies in the world, and it is undeniable that many ordinary Cubans want those freedoms, just as much as people in Iraq or Zimbabwe. Should they go on being denied them just because outsiders have a foolish tendresse for their elderly dictator?

It does not seem likely that Castro would have stayed in power so long without someone else to blame for his country's misfortunes, which successive US presidents, with their stupid embargo, have provided in spades. But two wrongs do not make a right and, far from being the island paradise depicted on travel posters, Cuba is a paranoid state where much of the population lives in fear.