Mary Kerry Kennedy was eight when her father, Robert F. Kennedy, was assassinated in a Los Angeles hotel in June 1968. The seventh of 10 children (the 11th was born six months after he died), Kerry Kennedy Cuomo is now the mother of three girls (four-year-old twins Cara and Mariah and one-year-old Michaela) and is married to Andrew Cuomo, son of the former governor of New York.

She is in London to talk to Vaclav Havel, the Czech president who spent years in prison under the communists. The previous week she was Spain to meet the lawyer for the 97 victims of the Pinochet regime, Juan Garcez, whose 30-year campaign for justice is about to reach a conclusion. The interviews are for a book she is writing on "human rights defenders". Since the birth of her children she has reduced her hands-on work as a human rights lawyer for the RFK Centre for Human Rights, which she founded in 1988. She now heads Amnesty International's leadership council, which has just launched a campaign against the abuse of human rights in the US.

First there is the death penalty. "We are the only Western country which uses the death penalty. We have executed 350 people since 1990, and there are 3,400 on Death Row. We use lethal injections, we use the electric chair, we use the gas chamber. It is so brutal." On February 4th, Sean Sellers will go to the electric chair for a murder he committed when he was 16; he has been on death row in Oklahoma for 13 years.

Then there are asylum seekers: "It's outrageous. America was built by immigrants, people seeking asylum. Every single American is an immigrant." She then raises the fact that America is the only country other than Somalia not to have signed CEDAW, the convention against discrimination of women and children. "We still shackle women while they're giving birth, for goodness sake." Then there's the thorny issue of arms. "We are the largest exporter of arms and training, etc to different militaries and different police forces and we need a code of conduct and we need enforcement mechanisms.

"The truth is that most Americans have no idea about what goes on. Police brutality is common in many of our urban centres and it's been around for years and years and years. The truth is that most of the brutality happens to people of colour. It doesn't touch the lives of people who are wealthy or educated. I think it's very important when a friend, a good friend, can point out one's weaknesses and you can start to work on changing them. I love my country and I hate to criticise it but look, I'd much rather see the problems and change them, than leave them. There is graffiti in the pyramids written by a slave from the time they were built saying: `No one was angry enough to speak out.' The way we are still treating people is just appalling. We have to be angry about it."

Seventy per cent of Americans still favour the death penalty, she adds. President Clinton has always backed it. While Governor of Arkansas he allowed a mentally handicapped man to be executed to support his "tough on crime" stance. But Kerry Kennedy Cuomo is, perhaps, uniquely qualified to defy the populist, vote-catching view: "As a family member of somebody who was murdered, there are no words to describe the pain of losing, in my case, my father to a senseless murderer, and the anger and fear that comes with thinking that the guy might be free and might do it again. So I understand people's reactions of anger and fear and seeking out the death penalty, if not as a solution, then at least as a salve."

She sits on the edge of the sofa, a slight figure in a neat, grey suit. In spite of the years spent in the public eye, she is nervous, hesitant. At 39, she is the same age her father was when he first stepped into the international spotlight, his delicate good looks outshining those of his burlier brother, the president. And there is something unbearably poignant in the set of her jaw, the curve of her mouth, and the way her thick hair stands away from her forehead - the resemblance to her father is inescapable. It was inevitable, she says, that she was drawn to human rights issues. "The idea of equality was always so important to me. I remember when I was learning to tie my shoes, I think I must have been four, I was always made sure that if I put on my left shoe first that I would tie my right shoe first. Because I wanted there to be equity. Now where does a little kid get that? Of course it came with my parents."

The Kennedy household at Hickory Hill was unconventional even by today's standards. "My father really didn't separate work from home; we were always going to his office and if we weren't there, the head of the civil rights division was staying at our house. And things were talked about all the time. Not only that, but we were very much expected to take part in it and we would sit around the dinner table and everybody had to mention something they had read in the paper today, which was really terrible if you were seated at the wrong end, because you know there were 10 of us so you had to make sure you were one of the first, not one of the last, God forbid, to come up with something good to say."

Kennedy Cuomo is intensely proud of her father's refusal during his presidential campaign to be deflected from campaigning on human rights issues. "He went to South Africa in 1966 when most Americans had never heard of apartheid. And he actually gave the greatest speeches of his life when he was there."

Better known, perhaps, is the speech he made following the assassination of Martin Luther King, which was no politician's oration, but a passionate attack on racism and inequality, using language that was 20 years ahead of its time.

Thirty years later, little has changed. Her father-in-law, Mario Cuomo, lost his seat as governor of New York after 12 years in office because he was against the death penalty. ("It was the major topic of the campaign against him. You have to be extremely brave as a politician to make that a focal point of your issues position.")

Kennedy Cuomo's first encounter with the rough hand of American justice was in 1981 when, as an intern with Amnesty International, she documented abuses committed by US immigration officials to refugees from El Salvador. As a young women brought up in the privileged world of east coast liberalism, it was, she says, a terrible shock. "I was overwhelmed. I was brought up to believe in America, Land of the Free. What was striking to me was the cruelty that my government, my government, was perpetrating. When I studied the Holocaust in sixth grade I thought, how could people do this? But I didn't know that it continued."

However, through working with lawyers who had taken on the cases of Salvadorans - for free - she was also struck by the possibility of change. "I realised how lucky I was to be living in a country that was capable of change. . ." Equally importantly, she enjoyed the campaigners. "They were the greatest group - bright, articulate and effective." Next stop, law school.

With the RFK Human Rights Centre, Kerry Kennedy Cuomo was able to draw attention to human rights abuses throughout the world, through an award given to an individual "who had stood up to government pressure, imprisonment or death, for the right of people to participate in economic and political decisions that affected their lives. We would then work with the people and develop programmes that would carry on their work. And it was great; it wasn't like standing in the First World and saying: `Well, the problem is torture and we're going to work on torture in your country.' Rather, it was seeking out the best and the brightest in the country and saying: `How can we be most helpful to you and how can we make you more effective?' "

Despite the chance of a safe seat on Boston's city council, she decided against taking the political road. "When my brother Joe ran for Congress I helped run the campaign. And it was great. But my heart and soul wasn't in (that line of) politics. It was really in international human rights. If you're a senator you could spend some of your time on human rights, a congressman a bit less of your time, but a city councillor, no - it's the sewage system." If she needs a political fix, she hasn't far to go: her husband is secretary of housing and urban development in the Clinton cabinet.

Husband, father, brother, uncle, father-in-law. As she says, a touch ruefully: "There are plenty of politics in my family to go round." Yet she soundly refutes the idea that Kennedy women are little more than iconic figureheads. "Eunice virtually revolutionised the way people with mental retardation are regarded and treated; Jean Smith helped to change the US approach to Northern Ireland: traditionally the US ambassador to Ireland kept a hands-off attitude to the North. Gerry Adams is not my favourite person in the world, but it took incredible courage and vision for her to say that he should be allowed to have a visa to visit the United States, because it was such a controversial decision, but it really started the peace process." And then of course there's her sister Kathleen, just re-elected as lieutenant governor of Maryland.

Meanwhile, Kennedy Cuomo's own sights are focused on her baby girls. In 1988 she was an election observer in the plebiscite which ousted Pinochet, and a poster from the anti-Pinochet campaign now hangs in her daughters' bedroom. "It's this wonderful poster that says `No', a big N-O. And it's got sunshine, and a rainbow and it's so full of joy and I think so important for girls to feel that `No' is a good word, that it's not bad to say `no'. Don't you?"