More than three years ago, as George Bush and Tony Blair rushed headlong into the invasion of Iraq, Martin Bright, then at the Observer, tested the veracity of an e-mail passed to him and his colleagues anonymously, while I nervously waited to see if the contents would appear in a newspaper. The e-mail, which the paper duly published, contained details of a bugging operation designed to coerce wavering members of the UN Security Council to vote for the use of force. It alerted the world to what I saw as scandalous dirty tricks within the United Nations.
I was sacked from my job at GCHQ, the top-secret government eavesdropping centre, and prosecuted under the Official Secrets Act, though the government dropped the prosecution when it was put under pressure to reveal the legal advice that took Britain into war. My aim had been to bring into the open government manoeuvrings and lies which were aimed at securing public support for what I believed was an unjust war, one that would lead to the deaths of thousands, and the untold misery of millions.
Had the case gone ahead, I would have argued that my action was intended to prevent an immediate threat to life. But I knew at the time that there was no automatic "public interest" legal defence for whistleblowers such as myself.
Fortunately, other civil servants were not deterred by my prosecution. My leak was followed by others and, bit by bit, the truth about Iraq has emerged - that there were no WMDs; that regime change was always the intention; that there was no al-Qaeda link. The bravery of other officials and public servants has since made us aware of renditions, torture, secret prisons and beatings.
Now, we face the dreadful possibility of action against Iran. Jack Straw may sincerely believe that "the idea of a nuclear strike in Iran is completely nuts", but we in Britain need much more detailed information of the sort that Seymour Hersh and other journalists have been revealing if we are to avoid following the US into another disaster.
This time, the talk is of mini-nuclear weapons, so-called low-yield ground-penetrating bombs. But even if Bush does not declare all-out war on Iran, any act of aggression towards that country threatens to plunge an already angered and turbulent Middle East into further chaos and inevitable bloodshed. And, how ironic that the US solution to Iran's nuclear ambitions should be to threaten to use nuclear weapons against them.
Truth-telling and whistleblowing were crucial in allowing us to piece together the facts about the lead-up to the invasion of Iraq. But it came too late to save lives in that war.
Whistleblowers have no immunity from prosecution, as I learned. Yet to me it would be a worse crime to remain silent about lies and misinformation that could lead us down the same path to an even more terrible war, or not to disclose information about planned aggression, legal advice, meetings between Downing Street and the White House, or JIC assessments of Iran's threat level. As the political momentum builds towards a military "solution", we must hope that this time we do not have to wait until the bombs have fallen and the lives of innocent families been destroyed before we learn the truth.
I was asked recently how I chose between the public interest and the national interest when I made my disclosure. I believe there was no choice, because in essence, the two are the same. The Iraq war has cost this country dearly, in financial and human terms. It has lost us credibility around the world. Not only does the majority of world opinion believe the invasion of Iraq was illegal, but Britain has been seen as acting aggressively and cruelly during the occupation. Avoiding such international dishonour would have been in the public and national interest.
The Vietnam war whistleblower Dan Ellsberg once said: "Like so many others, I put personal loyalty to the president above all else - above loyalty to the constitution and above obligation to the law, to truth, to Americans, and to humankind. I was wrong."