The Big Question: What is Scientology, and why have Tom Cruise's claims for it rebounded?

Why are we asking this now?

Millions of people around the world, it is said, have this week watched a nine-minute video of the Hollywood actor Tom Cruise enthusing wildly about his faith in Scientology. Cruise and his co-believers keep lobbying internet bosses to remove it, but as fast as it goes down it is gleefully uploaded by one user after another. Cruise doesn't like it because it is a collection of incomprehensible snippets spliced together to make him and Scientology look wacky.

So what exactly is Scientology?

That's complicated. It starts out as a mental health/self-improvement technique. You begin with a "free stress test" on the high street, which diagnosed me as unstable, depressed, nervous, irresponsible, self-critical and withdrawn. If you take the bait, you are then offered a session of "auditing" in which a Scientology "E-meter" (which a US judged once described as "of no proven usefulness") reveals to your Scientology counsellor just how bad you are. A system of intensive, and expensive, counselling called Dianetics will then purge you of "engrams" – undesirable thought patterns resulting from misdeeds in past lives. The higher up the auditing levels you progress the closer you get to the state that the Supreme Being intended.

Does it work?

Lots of people think so. Various Hollywood celebrities have told interviewers how it gave them an important set of life skills or improved their marriage. On the other hand, those for whom it has gone terribly wrong have ended up in courts where judges have said of Scientology that it is "corrupt, sinister and dangerous" or that it is a "schizophrenic, bizarre, paranoid... organisation that harasses its enemies and abuses the trust of its members". Even so it claims to be the world's fastest growing religion.

How many people are Scientologists?

Like everything to do with Scientology that's controversial. Last year it claimed 3.5 million members in the United States alone but independent sociologists said the true number was more like 55,000 people. There may be 100,000 worldwide.

In what way is it a 'sci-fi religion'?

It was founded in the 1950s by a former science fiction writer, L Ron Hubbard. The belief was that human souls were the ghostly remnants of aliens known as Thetans who had been brought to the Earth millions of years ago by a cruel Galactic despot named Xenu and his evil minions (who lived on as Christian clergy and psychiatrists). Scientologists today claim this is a wilful misreading of a metaphorical understanding of the human soul as an immortal spiritual being (termed a Thetan) which has lived through many past lives and continues after death.

Auditing, Hubbard claims, can allow individuals to reach through to this pure state and become an "Operating Thetan" as native spiritual abilities are recovered. Scientology is in practice a jumble of hypnotic techniques, Freudian theories, Buddhist and Hindu concepts, Aleister Crowley-style occultism and Gnosticism.

Just who was L Ron Hubbard?

The erstwhile pulp science fiction writer Lafayette Ron Hubbard claimed to have been an acclaimed explorer, a nuclear physicist and a war hero. He was none of those according to Russell Miller, author of a biography called Bare Faced Messiah. He dropped out of college with failing grades, never saw combat and had two bigamous marriages. An American judge once said Scientology mirrored Hubbard's schizophrenic and paranoid personality. As a sci-fi writer he once said: "Writing for a penny a word is ridiculous. If a man really wants to make a million dollars, the best way would be to start his own religion."

Has it made much money?

Sociologists who have studied it say that someone who works their way through all its levels will spend between $300,000 and $500,000. In the UK the Cult Information Centre knows of people who have spent "tens, if not hundreds, of thousands of pounds" trying to free their inner Thetan. But you can make money out of it too. Scientology pays members commissions on any new recruits they bring in.

Does it do any good?

Scientology volunteers have begun turning up to "assist" wherever natural disasters strike. Their website carries reports from two just back from an earthquake in Peru. They run an anti-drug programme called Narcinon, which involves exercise, saunas and vitamin B. The British advertising watchdog has criticised a Scientology advert which claimed it had rescued a quarter of a million people from drugs but accepted that the church had helped many addicts.

So is it a cult?

Scientologists vehemently deny this. In the United States the Cult Awareness Network, which was for 20 years America's best-known source of information and advice on religious cults, thought so. But the Scientologists took so many legal cases against it that legal fees forced the Network into bankruptcy. Whereupon the rights to its name, logo and hotline number were bought by a Scientologist who continued the organisation, but now staffed by Scientologists.

Does it behave like a cult?

It splits people from their families. Members send their parents letters saying: "At present I am not interested in receiving your calls, emails or letters, and if you do send any, I will view it as harassment and I won't bother reading them so please don't waste your time." Scientologists call that "disconnect" and say it is a rare last resort. Those who have quit say it induces "sensory deprivation and sensory overload, guided imagery and visualisation, trance induction through repetition of words or slogans...". It cuts members off from both external information and inner reflection. It creates a mystique of importance around the group and its leader – Hubbard is known as "The Source".

How does it handle criticism?

In the early years Hubbard issued in writing a policy that enemies of the church were "Fair Game". They could be "deprived of property or injured by any means... tricked, sued or lied to or destroyed." The organisation claims that policy has been revoked. But it routinely tries to close down critics on the web. In 1995 it tried to shut the internet newsgroup alt.religion.scientology. It has tried legally to force search engines such as Google and Yahoo! to omit any webpages critical of Scientology from at least the first few search pages.

Journalists who have investigated the organisation – Hubbard called them "chaos merchants" – have found themselves sued, harassed, smeared, and followed.

Is Scientology a force for good in the world?

Yes...

* It is essentially a self-help organisation that makes people feel good about themselves

* It runs programmes to help drug addicts and criminals

* Even if its sci-fi elements are wacky they are essentially harmless

No...

* It is a sinister, manipulative money-making cult that is dangerous and divisive

* It cuts members off from their families

* It harasses its enemies and abuses the trust of its members