Mordechai Vanunu, 50, is reviled as a traitor, has been disowned by his own parents and is a hero of the global anti-nuclear movement.

One thing that opponents and supporters agree on is that he showed incredible determination by surviving 18 years in a prison run by Israel's secret security services – the first 11 of them in solitary confinement.

Vanunu, the man who told the world about Israel's nuclear weapons programme, almost refused to walk free from prison today after declining until the very last moment to supply authorities with the exact address of where he was going to live.

And far from showing contrition when he did exit the gates, he told a scrum of reporters that he was "proud and happy that I did what I did".

His ironically titled poem I am Your Spy, composed in prison, bears eloquent testimony to his belief that he has been invested with a mission to save the Middle East from nuclear catastrophe.

"I have no choice. I am a little guy, a citizen, an ordinary fellow, but I will do my duty. I have heard the voice of my conscience. And there's nowhere to run," he wrote.

Vanunu, who has been nominated more than once for the Nobel Peace Prize, settled in Israel as a boy when his devoutly Jewish family emigrated in 1963 from Morocco. His parents had been well-to-do business people there.

After three years of national service, seeing combat in the 1973 Middle East war, he went to work at the secret Dimona nuclear plant in the southern Negev desert in 1976. He passed rigorous security tests.

Often working nightshifts, he found time to study philosophy and geography at the nearby University of Beersheba where associates say that he began his drift to the Left, becoming increasingly active against Israel's ill-fated 1982 war in Lebanon.

He was dismissed from Dimona in 1985 for "instability", but when he left Israel there was no sign that he was regarded as a security risk. He went backpacking around the world, carrying with him photos taken inside Dimona.

His dealings with the media began in Australia where he contacted Newsweek magazine and said that "for the good of the world" he was ready to sell a story about Israel's nuclear capacity.

He later broke off discussions because, he said, he was "too frightened to go ahead".

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