Astrologers would be as good as the spooks

How did they get it so wrong? It is now clear that the British and US governments perpetrated the most monstrous fraud on their peoples when they put the case for war in Iraq. No matter how much Tony Blair twists and turns, the truth was almost the opposite of what he and George Bush stated. Saddam Hussein was not an imminent threat. Stockpiles of chemical and biological weapons had long ago been destroyed. The UN inspectors, far from being gullible incompetents, gave an accurate picture. The best that Mr Blair can now say is that Saddam's ambitions made him a long-term danger and that he was still in breach of a number of UN reso-lutions. But the case for war argued urgency; that was supposed to be why we could not wait on the inspectors or wait for the UN to decide that the breaches warranted invasion.

We should not be surprised, though, that the security services and the politicians between them got it wrong. They nearly always do. As John Kampfner writes on page 8, the western intelligence services failed to predict almost every significant world event of the past 60 years. Astrologers might have made a better fist of the job. But we need to go deeper to understand why intelligence is such a dodgy business and why politicians who refer to it should always (regardless of their sincerity) be distrusted. It is now open season on journalism, but intelligence is more speculative than the wildest Andrew Gilligan report and, because even the end product is secret, far less open to scrutiny.

All the talk of an "intelligence community" and "professional assessments" suggests something like the GPs at your local health centre. In reality, intelligence involves bribery, theft, threats and double-dealing. It is like the five-day weather forecast: a vague guide, but not to be used for planning anything important. For Mr Blair to ask Lord Butler to inquire into "discrepancies" shows that he doesn't really understand intelligence, which has discrepancies in its DNA. Agents, as the now released Soviet files show, pretend to be better informed and connected than they really are. Informants have inscrutable motives: all but a handful of the East German moles recruited by the CIA during the cold war turned out to be double agents. Intelligence bosses (sub- consciously?) often tell their political masters what they want to hear, and get away with it because their claims are unverifiable and they themselves unaccountable. Like all who work in closed worlds, intelligence folk are prone to collective obsessions and fantasies, which once included the belief that Harold Wilson was a Soviet agent.

Western intelligence has a history of failing to understand the psychology of dictators. There is no mystery as to why Saddam should have allowed the false impression that he had WMDs to persist. A dictator prides himself on his strength, hoping to frighten both his domestic and foreign enemies. Allowing UN inspectors to roam his country unhindered would - as well as adding to the tyrant's inevitable paranoia about spies - have been a shame and humiliation, and entailed more transparency than a totalitarian regime can tolerate. To remain America's chief enemy was to Saddam a badge of honour. Sanctions, as opponents of the policy pointed out, strengthened him by weakening commerce and making the Iraqi people more dependent on the regime. In any event, like Mr Blair, Saddam was all too ready to deceive himself, and no adviser would have dared tell him of his weakness. It is all very well employing sound, rational chaps to work out what a dictator is up to, but dictators are not rational.

Democracies and dictatorships all too easily collude in what has been called "threat inflation". Democracies talk up the other side's strength - in order to convince their electorates of the need for higher defence spending. Dictators talk up their own strength - because they rely on fear to remain in power, not consent or negotiation. This lesson reverberates through the 20th century. In 1934, Churchill, relying on intelligence leaks, said Hitler had rearmed to the extent that Germany's air force was equal to Britain's. Hitler confirmed this to British ministers when they visited him the following year. Only after the war did it become clear that Churchill was wrong and that Hitler, at that stage, was bluffing. Churchill may have unwittingly helped the appeasers by publicising overblown estimates of German strength.

Documents released in Moscow since the end of the cold war show that both US and Soviet leaders persistently exaggerated the latter's strength and, as Noam Chomsky has pointed out, "when the world's two major propaganda systems agree on some doctrine, however fanciful, it is not easy to escape its grip". Then as now, the Pentagon and the US armed forces disputed CIA estimates of enemy strength, though the CIA itself usually overstated the position. For example, in 1961 - after a presidential election campaign in which John F Kennedy had made much of "the missile gap" - the air force reckoned Moscow had 200 ICBMs. The CIA put the figure at 50. We now know the Soviets had at most 44 ICBMs. The actual missile gap favoured America.

All this is troubling for those who hope for a more secure world. Stable democracies depend on public trust in leaders of any party to make honest, considered assessments of the national interest. It is not clear that Mr Blair deserves such trust. We had best cling to what ought to be self-evident truths. Wars should be fought only in response to tangible, immediate threats. People should be locked up only on tangible, testable evidence. Pre-emptive wars and pre-emptive detentions are the products of panic and fear, and these are the enemies of democracy.