However, what has fairly ripped my knitting in the weeks since has been the concerted efforts to give religion an alibi for the whole undertaking, depicting it as merely misused by extremists and clinging to the idea that faith itself is a virtue, all the while ignoring the very simple equation that no belief in an afterlife equals no suicide bombers. As Voltaire put it, once you can get men to believe in absurdities, you can get them to commit atrocities - and nobody has proved his point more vividly than those carrying out what is literally the ultimate act of faith.

The notion that faith - belief in spite of an absence of proof or even in the face of compelling contrary evidence - is a form of mental and moral fortitude needs not merely to be challenged, but to be given the full point-and-laugh treatment, so that we can see afresh how this absurdity deserves ridicule rather than reverence.

My new novel, Attack of the Unsinkable Rubber Ducks, takes its name from a coinage of the magician and sceptic James Randi to describe people who, no matter how much proof you try to submerge them in, always bob back up again with a new reason to keep believing. The liberal consensus - one I subscribe to - is that people should be free to believe whatever they like. However, with freedom always comes responsibility, and thus people should be responsible enough to avail themselves of the facts and, where necessary, adjust their beliefs accordingly.

To illustrate, the book deals principally with belief in the idea that it is possible to communicate with "the other side", a notion that has intermingled with modern Judeo-Christian faith in an afterlife. It remains a very popular belief: even otherwise rational people, while scorning Derek Acorah and what they perceive to be the cheesier end of mediumship, will none the less say they think there must be something behind spiritualism. There is: it's called the phalangeal joint, and the disparaged "cheesy end" is in fact the centre, the root and the whole of spiritualism.

The modern concept of mediumship began in 1848, in Hydesville, New York, the product of two pubescent sisters, Margaret and Kate Fox, who exploited a shared ability to crack their toe joints against wooden floorboards to create rapping sounds that put the wind up their highly superstitious mother. The two girls soon found themselves the centre of unprecedented attention.

Their much older sister, Leah, took one look at her younger siblings' antics and saw dollar signs. She swiftly founded a Society of Spiritualists in order to add gravitas and mystique to a series of profitable public performances. Leah took her sisters on a grand tour of American cities, but spiritualism was spreading far faster than the steam trains could carry it, with imitators and variants rapidly staking their claims.

The younger Fox sisters found themselves clinging to a rising balloon, their silly wee prank now a quasi-religious cause attracting such celebrity adherents as the late president's widow, Mary Todd Lincoln, and even Sir Arthur Conan Doyle. Despite the altitude, on October 21 1888, Margaret let go. That evening she gave a lecture at New York's Academy of Music, having earlier in the day published an article in which she confessed the truth. The 2,000 spiritualists present angrily jeered her, not for having deceived them, but for her "lies" in the article. Margaret's submission of hard contrary evidence did nothing to prevent the spread of the movement and associated beliefs.

One of those was Helena Blavatsky's cult of theosophy, which used its supernatural mystique as an underpinning for a racial mythology in which a group called "the Aryans" were "the Race of Hope". This was seized upon by Nazi theorists, including Heinrich Himmler.

An extreme example? Go back and read again what Voltaire said regarding absurdities and atrocities. All of this from two little girls trying to scare their mother with their percussive toes. The story of the Fox sisters and the rise of spiritualism illustrates that belief in the face of the evidence is at best a retreat into intellectual infantilism, and at worst dangerously irresponsible.

The Glasgow would-be bombers believed faith itself was a virtue, a sufficient reason to murder hundreds of innocent people. I don't think being nine hours too early on June 30 disqualifies me from saying that such faith is a self-indulgence we can ill afford.

· Christopher Brookmyre's Attack of the Unsinkable Rubber Ducks is published this week

christopher_brookmyre@yahoo.co.uk