If you are now or ever have been a member of the Spice Girls, there maybe something missing from your life. You will have money, fame, and a body which can bishop do a backflip through a stained glass window. But when these pleasures pass, a threatening doubt remains: does anyone really understand your inner life? Does anyone even believe you have one?

The answer to this problem is the same as the answer to every other problem conceivable to a celebrity: you need a photographer. Fast. And a book. To be photographed carrying a book is the ultimate demonstration of intellectual stature in this world. To be photographed with two different books in one week, as Geri Halliwell has been, is to make a really unmistakable statement that you are now a Serious Person.

Except that the second book she was photographed with in her intellectual Odyssey was no ordinary self-help manual. It was the Scientology Manual, the handbook of one of the nastiest religious organisations of the Twentieth Century. Scientology, founded by a megalomaniac science fiction writer named L Ron Hubbard to separate fools from their money using the latest modern technology.

In this Hubbard was enormously successful. He died rich beyond the dreams of avarice. In 1982 alone, his biographer estimates, he made more than $40m off the various Scientology corporations. The cult made strenuous efforts to suppress this biography and as is usual with hostile journalists even put private detectives onto the author.

His is the only religion I know which has copyrighted its scriptures as trade secrets. But then it is the business of selling enlightenment. Though the early ideas are given away, the inner secrets cost. Devotees must pay anything up to 100,000 to learn the grotesque details of his mythology: my favourite is the idea that wicked alien spirits attach themselves to believers in the shape of body hairs.

So: the scientologists are rich. They're paranoid. They peddle nonsense. They have invented a religion that really speaks to the condition of the modern celebrity. A startling number of Hollywood stars have announced themselves as scientologists. Tom Cruise, John Travolta, Lisa Marie Presley and Kirstie Alley from Cheers are  the most famous. If Geri Halliwell goes the whole way and actually opens her book, she will find herself in some fairly distinguished company.

What is mysterious is why they prefer scientology to any of the other cults and religions on offer. Not all do. The martial arts specialist and start of extraordinarily violent films, Steven Seagal, has given so much to Buddhist causes that one unusually discerning Lama has realised that the actor is in fact himself a reincarnated spiritual teacher.

But Buddhism has problems of its own. It is crowded. The highest position open to any star turning towards the religion is that of Second most Famous Buddhist after Richard Gere, and many people feel that this does not do full justice to their spiritual capacities. Then there is a certain amount of nonsense about celibacy. It's no use being so spiritual you can't get laid.

Scientology, on the other hand, is the Rolex of cults. Consumption doesn't get more conspicuous than this. To be a celebrity scientologist proclaims, firstly, that you have a lot of money. You can spend more on self-discovery than your friends have spent on swimming pools. Or cars. Or even on swimming pools with cars inside them.

Secondly, to be a celebrity scientologist proclaims that you have sanity to burn. There you are, convinced that we are all pawns in a power struggle between gigantic extinct alien empires; that harmful memories implanted by these aliens are holding you back from reincarnations, and that L Ron Hubbard was a the greatest genius the world has ever seen and still you can function and earn a living. This proves you are far cleverer than almost everyone else in the world.

But the final benefit of scientology for the star and the would-be star is one that no other belief system can offer. It lies in their most enduring hatred. The people the scientologists hate most are not mocking journalists; and possibly not even the tax authorities. They are not the ex-members who have been pursued by lawyers and private detectives half way round the world. They are psychiatrists. Scientologists know that psychiatry is one giant conspiracy against the human race. And any religion that holds that psychiatry is evil would be bound to flourish in California. It's too original to fail.

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