It is nearly 10 years since Olga Salanueva and Adriana Perez last saw their husbands. René González and Gerardo Hernández are in jail in Marianna, Florida, and Victorville, California, members of the so-called Miami Five, all serving sentences stretching to double life for "conspiracy to act as a non-registered foreign agent".

Olga Salanueva Arango (L) and Adriana Perez O'Connor, wives of two Cuban nationals arrested and jailed on charges of intent to commit espionage and threatening US national security. (Photograph: Frank Baron) Salanueva and Perez are in Britain this month to talk to members of the government and to anyone else who will listen about a story that is a cause célèbre throughout Latin America but is virtually unknown in the United States. It is a story that in many ways encapsulates the conflict between Cuba and its mighty neighbour for the past half-century and has ramifications both for the current "war on terror" and for the US presidential election campaign.

Ever since the Cuban revolution that brought Fidel Castro to power in 1959 there have been attempts by exiled Cubans, often with the assistance of the US government, to remove him. Famously, the CIA was involved in a number of bungled assassination attempts, although they have pulled back from this tactic in recent years. The Cuban government claims that more than 3,000 people have died as a result of various plots, from the failed 1961 Bay of Pigs invasion to the more recent attacks, such as the bomb placed on a Cuban plane in 1976, in which 73 people were killed, and the explosions in Havana hotels and clubs in 1997 that attempted to derail the booming Cuban holiday industry. Such plots have usually been hatched in Miami and it was the groups based there that five young Cubans, two of them born in the US, infiltrated in the 90s. Their plan was to report back on the groups' activities.

In 1998, the five were arrested and effectively accused of espionage. The US government argued that they were acting as foreign agents and should be treated as spies. The five argued that they had been trying to prevent terrorist attacks. A trial was held in Miami in 2001, despite legal objections that they would be unable to get a fair hearing there because anti-Castro sentiment was so rife. The five, González, Hernández, Antonio Guerrero, Ramón Labañino and Fernando González, were convicted and sentenced to terms varying from 15 years (René González) to double life plus 15 years (Hernández).

With the help of a legal team headed by the veteran American civil rights lawyer Leonard Weinglass, they appealed and, remarkably, in 2005 won the right to a retrial outside Florida. But the prosecution appealed, the retrial was stalled and the case is now due to go to the supreme court in December. In the meantime, the two women have never been allowed into the US to see their husbands. As Perez's husband is serving a double life sentence, she will never be allowed to see him alive again.

"They give us different arguments every time as to why they will not give us a visa," says Perez, 38. "They have alleged that we may be a threat to the security of the US or they say that we might be meeting terrorist organisations on US territory. Or they say that I am a potential immigrant, so I can't enter the country. It changes every time. In Olga's case, she was deported from the US when her husband was arrested and so they say she will never be eligible for a visa. What it means is that our husbands are serving an additional sentence in that they are not allowed to see us. And for Gerardo and me, it is like a life sentence. It is a form of psychological torture."

Perez says that, after the initial arrests of the five, attempts were made to persuade them to plead guilty or inform on their co-defendants and on Cuba by threatening to block access to their families if they did not cooperate. "They have used the families as a sort of additional tool to blackmail them and weaken them," she says. She was granted a visa in 2002 but, on arriving at Houston airport, was detained and refused permission to enter the country.

"We keep in touch by letters and telephone calls but they are limited to a number of minutes," says Salanueva, 48. At the time of the arrests, their two daughters, Irma and Ivette, were aged 14 and four months. Now the older daughter is a qualified psychologist. "I have applied to see René nine times and been refused nine times. A number of members of the family have died since he was in prison and we have not been able to let him know directly." She said that the five, who are all held in different prisons scattered around the country, have adjusted to life in jail and do not have problems with the other inmates. "They have good relations with the other prisoners, I think they have a lot of respect and they are able to help the others with their documents and appeals and things like that."

While it would be impossible to be unaware of the case in Cuba, where massive roadside billboards of the men are part of the landscape, the case has received remarkably little coverage in the US, although there are support groups there, the most active of which are in San Francisco. "We have come up against a wall of silence in America," says Salanueva. "It is very difficult getting the information out, so people really don't know anything about it."

They do, however, enjoy support from a variety of writers, artists and public figures in the US and around the world, including Harry Belafonte, Desmond Tutu, Harold Pinter, Nadine Gordimer, Danny Glover and José Saramago. Amnesty International has called on the US to review the decision to refuse the women visas to visit their husbands. "Denying the men visits from their wives . . . is unnecessarily punitive and contrary to standards for humane treatment of prisoners and states' obligations to protect family life," said a spokesperson. The UN commission on human rights has also called into question the nature of the trial, which "did not take place in the climate of objectivity and impartiality that is required" (under the international covenant on civil and political rights).

Few American politicians would risk espousing such a cause and certainly not on the eve of a presidential election in which Florida voters could once again play a key role. The Cuban exile population in the state still carries great political weight, although that influence has been waning for the past few years as a generation that feels less strongly about Castro emerges. Attitudes towards Cuba have changed in some sections of the US in recent years and members of both main parties have indicated that it is time for talks and rapprochement. So, after the election, might Barack Obama, who has made noises about talks, or John McCain - himself a former prisoner - be more receptive, at least to humanitarian pleas for access?

"We do not have great hopes in a change of power," says Perez. "There have been many changes of administration in the United States over the years but the attitude towards Cuba has always remained the same."

What makes the Miami Five case doubly relevant now is its connection with the "war on terror". Before the arrests of the five - before September 11 changed the focus - the FBI actually contacted Havana to ask for intelligence on any planned acts of terrorism directed at Cuba in which US residents were involved. This is not as unusual as it might seem; the two countries cooperate on disrupting drug trafficking in the region. The Cuban government thought that there might be a possibility of doing the same on plots to attack Cuban targets, but the arrests ended any such notion. Now relations between the two countries are as frosty as ever, not least because Luis Posada, the man whom the Cubans believe was responsible for the Cubana airliner attack more than 30 years ago, is still a free man in Miami, requests for his extradition to stand trial having been refused.

So tomorrow, Perez and Salanueva will be protesting outside the US embassy in London on behalf of men they have not seen for a decade. "What they were doing in Miami was fighting against terrorism," says Perez. "They were trying to save lives and now they are being punished for it. There is something very wrong about that".