Almost 18 years ago, I flew halfway round the world - to Sydney in Australia - to meet a man who had taken a momentous decision. Mordechai Vanunu, a former worker at Israel's Dimona nuclear research centre, had decided to blow the whistle on his country's biggest secret.

Although Israel refused to acknowledge it, Dimona manufactured nuclear weapons in an underground factory in the Negev desert. I had learned Vanunu was willing to talk and that he had taken photographs inside the most sensitive section of all, the area separating out plutonium from uranium fuel rods. My assignment held out the hope of puncturing Israel's duplicity: a public posture that it would not be the first to introduce nuclear weapons into the Middle East while clandestinely producing them on a large scale.

Arriving in Sydney, Vanunu immediately impressed me as a careful and honest witness. He was candid about what he knew and what, as a technician, he didn't. He said he had become alarmed at the quantity and sophistication of the weapons being produced. What compounded his concern was that the Israeli public and the Knesset (parliament) were being kept in ignorance.

Had Dimona been producing just a handful of atomic bombs - enough in extremis to deter an enemy threat - I doubt if Vanunu would have become a whistleblower. But in the 1980s, the activity in the hidden complex where he worked had changed and become much more sinister. Other than producing plutonium, the plant had begun making tritium and lithium 6; Morde knew this meant something far more significant: Israel was developing neutron and hydrogen bombs. Coupled with public disclosures that Israel was developing ballistic missiles, it was evident to him that Israel was becoming a fully-fledged nuclear power with the capacity, if not the inclination, to wage an offensive war far beyond its borders. Nor was this small scale. He knew that scores of warheads had been fabricated (we eventually calculated between 100 and 200).

Given that this had no public mandate in Israel, Vanunu believed, and still believes, it was irresponsible, dangerous and immoral. He believed that disclosing what he knew would help the peace process in the Middle East. By speaking to a newspaper with international reach like The Sunday Times , it never occurred to him he was being a traitor to his country and a spy, as he would later be branded. His aim was to generate public debate in Israel on the WMD issue, something that the media had never dared do previously.

After debriefing him in Sydney for nearly two weeks, Vanunu and I flew to London for his story to be checked by experts. He realised the danger of what he was doing, but we had no idea that Mossad, the Israeli secret service, was then on our trail. I have since learned that a hit-team was already under orders to follow him. At the same time, they were instructed do nothing in London that might damage the harmonious relationship between Britain's Prime Minister, Margaret Thatcher, and Shimon Peres, her opposite number in Jerusalem. After nearly three weeks of further debriefings here, Vanunu became irritated with his Sunday Times minders. He was also upset that the paper had delayed publication of the story to seek further verification. He began to take walks on his own and, one fateful day in Leicester Square, he casually fell into conversation with a US tourist who called herself Cindy.

They dated two or three times and Cindy suggested a holiday in Italy. On 30 September 1986, they flew to Rome. As is now well known, it was a terrible mistake. He had walked full tilt into a honey-trap, sprung by Mossad, and these were his last moments of freedom.

Cindy, a well-trained Mossad agent, took him to an apartment where two men grabbed him and manhandled him to the ground, clasped handcuffs on his arms and legs, and injected him with a sedative. That night he was smuggled onto a boat off the coast of La Spezia and taken to Israel. Tied to a stretcher, he was landed on the beach at Tel Aviv and taken to an interrogation centre. Someone thrust a copy of The Sunday Times into his hands showing his story spread across three pages. It must have given him some satisfaction that his story was out, but there were other emotions: what were they going to do with him? Kill him and dispose of him quietly?

If it had not been for the international publicity generated by his disappearance, I suspect Vanunu would have been tried in secret and locked away without anyone except his family knowing of his fate. A brother was visited by agents and told that he was safe but that he would never see him again. However, faced with having to disclose he was in Israel, the authorities produced Vanunu in the Jerusalem District Court and charged him with treason, espionage and breaches of the official secrets act. The trial was held in camera but I was able to give evidence in his defence. I tried to tell them this man was no traitor, nor spy. He did not sell secrets to a foreign power and he was not spying for one. I said he had acted out of principle to expose something that was harmful to his country. Any action he had chosen to take in Israel would have led to his arrest and, by talking to me, he had placed the facts openly before everyone including the Israeli public. I added that Israel had not been made militarily weaker and, arguably, was strengthened by his disclosures.

I was asked at one point if I was aware Vanunu had converted to Christianity in Australia. I could see no relevance in this but answered that he had never made a secret of it. I was taken aback when the prosecution responded: "So you knew he had turned against his family and his country."

The court adjourned and, later in 1987, sentenced him to 18 years. Whether the stigma of his conversion affected the decision is not known, but it has always inflamed the Israeli press. Few joined the campaign to help him and the numbers have remained low.

Vanunu spent nearly 12 years in solitary confinement. For the first two-and-a-half years, his cell had no natural light and a fluorescent tube remained on 24 hours a day. With just occasional visits from some of his family, most of whom have rejected him, his mind began to go, as evidenced by his letters to me.

In 1997, after much lobbying and campaigning, and the support of a couple of Israeli Knesset members, he was allowed to leave solitary. His mental health improved quickly and today he is well and optimistic about his release. But as we became aware last year, the notion that he would be freed unconditionally on his scheduled release date of 21 April 2004 was not a forgone conclusion.

Reports began to circulate in Israel last year that the authorities might prevent his having contact with anyone who could not be trusted. These reports were given added weight in January this year when we learned the ministry of defence were seeking ways to keep him in administrative detention under a little-used emergency law dating back to the British Mandate. If that failed, he might be kept under house arrest and barred from leaving the country.

In late February, however, a spokesman for Ariel Sharon announced that Vanunu would not be placed under administrative arrest or house arrest. The defence ministry said some monitoring mechanism would be established - probably surveillance and telephone tapping - and that he would not be given a passport. By early-March, a small degree of common sense appeared to prevail, but the threat of a passport ban remains. Vanunu wants to settle in the US with a couple who have legally adopted him. But wherever he lives, the only damage he could do is remind the world that Israel's nuclear policy is based on a lie; make life uncomfortable for Israel and its allies; and expose the double standards of the West in what is supposed to be a uniform stance against nuclear non-proliferation.

Meanwhile Israel has been left free to demonise him. Had Vanunu been, say, an Iraqi or an Iranian whistleblower with evidence of nuclear secrets in these countries, who had come to The Sunday Times , been abducted and tried for treason in Baghdad or Tehran, it is hard to imagine the world's leaders remaining silent, as they have done in this case. They would, rather, have feted such people as heroes. Yet here was a man who had been locked away for most of his adult life after being kidnapped - a blatant offence against international law as well as the domestic law of Britain and Italy. Yet neither Britain nor Italy did anything in response. My only consolation is that in one important respect neither the kidnapping nor the imprisonment succeeded: The Sunday Times published the Vanunu story and, 18 years on, we are still talking about those disclosures.

Vanunu is a victim of a gross act of censorship for which Israel has gone uncensured. A victim, too, of the extraordinary duplicity of the West in turning a blind eye to Israel's nuclear capacity in the interests of preserving Israel's close relationship with the US. An open admission that Israel has a nuclear weapons programme would bring into play the Symington Amendment to the US Foreign Assistance Act, which forbids US military aid to countries illicitly acquiring nuclear weapons. Israel is still the biggest benefactor of US military aid. He has survived a terrible ordeal and triumphed over his enforced idleness for nearly 18 years; Dimona has not fallen idle. The reactor is still operating and so is the plutonium separation plant, the supply of which is the reactor's main purpose. One can calculate that Israel has made at least another 100 to 200 nukes since 1986 of ever-greater sophistication. It has taken delivery of three submarines from Germany capable of launching nuclear-armed cruise missiles. It has three-stage missiles with a range of many thousands of miles. It has thermonuclear weapons everyone one of which is capable of destroying an entire city.

Vanunu's crime is to have embarrassed Israel by exposing its policy of nuclear ambiguity: a policy that has enabled its nuclear build up to continue unhindered.

Published 2004-04-26