It is 50 years since Joseph Rotblat quit the atom bomb project, but this year's Nobel peace prizewinner is still tirelessly campaigning against the menace he once helped to create. Lucy Hodges went to meet him

At the age of 87 most people are happy to take a rest, put their feet up and grow tomatoes. Not so Joseph Rotblat, the Polish-born physicist who has made his home in London and this year won the Nobel peace prize with the Pugwash Conference on Science and World Affairs of which he is president.

This weekend Rotblat flies to Oslo to receive the award which he has won for his work on preventing a nuclear disaster. But he is only stopping over in Norway. On that same trip he is cramming in speeches in Sweden, and after Christmas he will be off to Australia to sit on a commission set up by the Australian government.

Rotblat is a compulsive worker. For the past 40 years he has laboured tirelessly to rid the universe of nuclear weapons. The general public may never have heard of Professor Rotblat or Pugwash, because he and it have gone about their business through more than 200 quiet conferences - on nuclear testing, anti-ballistic missiles, biological and chemical weapons.

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The meetings have been for the scientific cognoscenti from East and West, but their ideas have filtered through to governments via scientists and Rotblat believes they have hit their targets. The partial test-ban treaty of 1963, the 1972 anti-ballistic missile treaty, as well as the agreement not to develop biological weapons and the new agreement on chemical weapons - all have been helped along by Pugwash. With the cold war over, Pugwash has finally won recognition for those long years of unremitting effort.

That is a source of great satisfaction to Rotblat as he sits beaming in his threadbare office opposite the British Museum. "We achieved channels of communication between East and West," he says. "These channels helped to remove ignorance and prejudice."

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The setting up of Pugwash dates back to the mid-1950s when Bertrand Russell, Albert Einstein and nine other prominent scientists, including Rotblat, signed an anti-nuclear manifesto in Caxton Hall, London. It was the beginning of the cold war. Ballistic missiles were being manufactured. No one could forget the annihilation of Nagasaki and Hiroshima at the end of the second world war.

Rotblat himself was devastated by the destruction of Hiroshima by the bomb he had been working on in Los Alamos. "Since the defeat of Japan was obvious, I saw the destruction of Hiroshima as a wanton, barbaric act, and it made me very angry," he wrote in his reminiscences. "Even stronger than the outrage was the despair about the future. From my days at Los Alamos I knew that the fission bomb was only the first step in nuclear weaponry."

For the first time it had become possible for the largest city in the world to be destroyed by one bomb. The 11 men in Caxton Hall believed scientists should take responsibility for their inventions. They appealed to colleagues around the world to put aside their ideological and political differences for the common good. Such talk sounds utopian today, but reading the voluminous newsletters put out by Pugwash, one realises how technical and practical is much of the organisation's work.

"The characteristic of Pugwash is to pursue its objectives in a pragmatic way," says Rotblat in his written reminiscences. "Pugwash combines idealism with realism. We do not indulge in issuing populist declarations, slogans which may impress the public but without hope of being achieved."

Named after the small Canadian village where its first meeting was held, Pugwash resolved that only individual scientists could be associated with the organisation. No delegations were allowed because they got in the way of open and frank debate. "You make more progress with individuals," says Rotblat. "Delegates come with a brief."

The desire for honest discussion was the reason Pugwash did not open its doors to the press. It was not a secret society, says Rotblat, but it did want the eminent scientists who attended its meetings to speak their minds.

The first Pugwash conference - held in 1957 - was confronted with the knotty problem of nuclear testing. The United States had exploded a hydrogen bomb on the tiny island of Bikini Atoll and its radioactive fallout had showered a Japanese fishing boat with ash. One of the crew died. Rotblat began his detective work, discovering fairly quickly that the explosion of such bombs presented serious health hazards. He published his views, embarrassing the British government in the process. He has been embarrassing the British and other governments ever since.

Initially Pugwash's goal was the elimination of nuclear weapons, but the group soon realised that was an impossibility, given the intense cold war atmosphere and the build-up in nuclear weapons arsenals. So, it trimmed its aim to halting the arms race. Rotblat thinks this paid off. "Many of our people believed that Gorbachev's decision to call a halt to the arms race was greatly influenced by discussions in Pugwash and the exchange of information we had," he says.

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"Although I cannot provide factual evidence, there are good reasons to believe that our efforts in Pugwash contributed to the ending of the cold war."

Although Rotblat could be said to have achieved what he set out to do, he is not giving up. He rises at six every morning and does not turn in before midnight. You might wonder about his health. But he says he is perfectly fit, and he certainly looks bursting with vigour and good cheer. Moreover, he has lost none of the passion about nuclear weapons which has stirred him into action for much of his life.

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For example, the decision by the French president, Jacques Chirac, to engage in nuclear testing earlier this year outraged him. Pugwash wrote to Chirac in protest, and to point out that France was in breach of a moratorium on nuclear weapon testing which it had signed.

To what extent are Pugwash's ideas accepted by the nuclear powers in the aftermath of the cold war? One might think many countries would be coming round to them but Rotblat says he has not managed to break resistance to strongly-held beliefs. People still believe that nuclear weapons are needed for the security of the world. This argument - that nuclear weapons prevent war on the grounds that no one country would dare to use them because of the damage they do - is a hangover of the cold war mentality, according to Rotblat.

There is no evidence for the argument, he maintains. "I have always said the existence of nuclear weapons clearly causes war. We have had around 180 wars in the world since 1945."

One only has to look at the evidence, he adds. Nuclear weapons were used in Vietnam and in Afghanistan. They did not prevent war. And the nuclear powers did not win either. Despite possessing nuclear weapons, they lost both wars.

Nevertheless, he is optimistic. In the United States his argument is making headway. Pugwash's current objective of a nuclear-weapon-free world, is winning converts slowly. For example, General Charles Horner, chief of US space command, has said he wants to get rid of all nuclear weapons. Melvin Laird, former US defence secretary, has declared that should be his country's goal. And Robert McNamara, a Pugwash participant, believes in a return by all five nuclear powers to a non-nuclear world.

The biggest obstacle now to achieving this aim is the fear of "break-out" - the clandestine fabrication of nuclear weapons by one country which in a nuclear-weapon-free world would give it superiority over all others. "We have to provide convincing arguments that we can deal with the break-out problem, and this is what we are working on now," says Rotblat.

Despite his scientific background and his hatred of communism, Rotblat has been dogged with the "communist" label for much of the past 40 years, probably because he has been advocating ideas that are not government policy, he thinks. As a scientist with a conscience, he had been a thorn in the side of the nuclear powers since 1944, when he left the top-secret Manhattan project in Los Alamos where the Allies were making the atom bomb. He resigned from that project for ethical reasons. "I found out at the end of 1944 that the Germans were no longer going ahead with research into a bomb," he says. "The whole rationale for my work was no longer valid."

Amid considerable acrimony, Rotblat returned to Britain where he got a job working as a professor of physics at St Bartholomew's Hospital. He discovered that before he left America US intelligence officers decided he was a Soviet spy. They concocted a fantastic story that he intended to enlist in the Royal Air Force and parachute into Soviet territory to give away atom bomb secrets.

Rotblat always wanted to return to his native Poland, which he had left in 1939 just before the outbreak of the second world war to conduct research in Liverpool. But he never did return because he felt he could not work in a Soviet regime. It is ironic, he thinks, that critics like the Conservative peer Lord Beloff accuse Pugwash today of being duped by communist agents when the organisation has always set out to be above the ideological fray.

He accepts that foreign office minister Lady Chalker does not take the Beloff line. But he believes the reason John Major, the prime minister, sent him such muted and belated congratulations for the Nobel peace prize is that Pugwash does not toe the government line. The governments of Germany, Sweden and Japan sent him letters of felicitation. And Lech Walesa, the president of Poland, sent him a note congratulating him "with my whole heart". But John Major said nothing until adverse publicity forced him to do so.

Meanwhile the scientist says he is going to spend every penny of the $1 million award money on building up Pugwash. His organisation is run on a shoestring. It has always refused to accept government money, and has relied on small sums from national Pugwash groups and from one-off donations from foundations. Its latest book, for example, A Nuclear-Weapon-Free World, edited by Rotblat, Jack Steinberger, a physics Nobel prize winner, and Bhalchandra Udgaonkar, another physicist, was financed by the W. Alton Jones Foundation.

Looking back on his life, Rotblat observes that the Manhattan Project changed radically his scientific career and his attitude to his social obligations. It convinced him that even pure research soon finds applications. "I wanted to decide for myself how my work would be used," he wrote in an article in The Times. "I thereafter chose to work on an aspect of nuclear physics that would definitely be beneficial: to medicine."

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But he is left with a nagging thought. Would he ever repeat the mistake he made in the 1940s by returning to work on atomic warfare? Rotblat is not sure. "Not being an absolute pacifist, I cannot guarantee that I would not behave in the same way, should a similar situation arise."