A Ttp Scientologist who escaped the cult has given the most explosive insight yet into the shady "celebrity religion".
A-list followers including Tom Cruise, Kirstie Alley and John Travolta believe their faith is the secret of their success.
But for John Duignan it cost him everything and everyone he held dear after he become a leading figure in the church's British branch.
John says he was so brainwashed that he would have killed for Scientology.
And he claims another member was driven to a suicide bid when she was "rehabilitated" after trying to leave.
John tells of his nightmare in his book.
His hell began in 1985 when he was approached in the street by a pretty girl who offered him a free personality test.
John - who had never heard of Scientology - was 22 and living in Stuttgart with his German girlfriend but their relationship was on the rocks. Depressed and lonely, he accepted.
John, now 45, says: "The test is a clever recruitment device because it appeals to people who are searching for something. I was unhappy and latched on to the prospect of gaining confidence. I probably needed proper psychological counselling but I got nothing of the sort. The result of my initial test was Urgent Action Required.
"These friendly people seemed to have the answer in Scientology and I surrendered myself to it."
In the following weeks, John was grounded in the Scientology doctrine.
The movement was founded in 1952 by an American sci-fi writer, the late L Ron Hubbard.
He claimed humans are really spiritual beings called Thetans which have lived for trillions of years and are constantly reincarnating.
Followers believe that through past life recall therapy they can enrich their understanding and souls.
Under a regime of sleep deprivation, brainwashing and so-called counselling, John gave up his mind to the bizarre teachings.
He says: "On one occasion I sat on the floor while others shouted in my face and flicked things into my eyes.
"It went on for hours. I wasn't allowed to react or blink. You're suppressing your natural reactions and that helps Scientology creep in to take over your mind."
John quickly became fanatical about his new-found faith.
He says: "I saw myself as a soldier for Scientology. I believed it was the only route out of oblivion for mankind.
"The doctrine teaches a human's body doesn't matter because it is the Thetan, or soul, which survives.
"If I'd been told someone had to be eliminated because they were a threat to Scientology I could have justified the killing. They'd just lose their body, which isn't needed."
When it was suggested John might train to become a church staff member, he jumped at the chance.
He signed up for an "advancement course", where he endured constant "auditing" sessions, being grilled on every aspect of his life.
John says: "I was hooked up to a Scientology machine called an E-meter. It has a swinging needle and believers think it shows hang-ups or concerns.
"Your goal is to achieve no movement of the needle and a state of "Clear". That's when you're ready to receive the secrets of the universe.
"By now I had cut all ties with friends and family. I was trying to take Scientology doctrine on board but it felt as if my mind was being repeatedly hit with a hammer."
John persevered, and three months after his personality test he received a call from Scientology Missions International in Los Angeles.
They wanted him to join the church's 3,000-strong elite core, Sea Org, which oversees recruitment and its other big international interests.
For John it was his ticket to the Scientology big-time.
He says: "As a Sea Org member I'd get to wear a special uniform and be highly respected by other Scientologists. We were told other members would bow to us. Suddenly I felt important."
But when John arrived at the cult's headquarters in LA, conditions were not what he'd imagined.
He says: "We were expected to work, eat and sleep Scientology with every minute of the day scheduled, from 7am until lights out at 11pm."
The harsh conditions John endured were in stark contrast to the luxury enjoyed by stars at the glittering Scientology Celebrity Centre down the road.
L Ron Hubbard believed the church should have famous names as the church's public face.
John says: "The centre is beautiful. I loved it when I worked there in the garden. Once I spoke to Kirstie Alley on the phone about a rally we were organising. I also saw John Travolta a couple of times.
"But interaction with celebrities wasn't encouraged. They arrived through a special celebrity entrance and were taken to exclusive suites for auditing sessions."
After the Sea Org bootcamp John was posted to Scientology's UK HQ, Saint Hill Manor in East Grinstead, West Sussex.
Here he spent almost two decades devoting his life to the cult - until a bizarre encounter with Scientology poster boy Tom Cruise made John begin to question his faith.
He says: "In 2004 Tom was welcomed to the annual International Association Of Scientologists Gala Ball as the Most Dedicated follower.
"I was working in the grounds and Tom came out wearing a bad fake beard. It was pathetic.
"Scientologists look upon Tom Cruise as one of their best assets, but it was him who made me think twice about the cult.
"I was earning £15 a week, doing my best to spread the word. I had no privacy or time to relax and was afraid or stressed all the time.
"Yet I wasn't as dedicated as Cruise? It hurt."
Two years later John made his escape bid.
He says he knew he would be hunted by the sect's intelligence wing, the Office of Special Affairs (OSA).
John says: "Members who try to leave Scientology are subjected to the Rehabilitation Project Force.
"This uses military tactics and are feared. A friend, Alice, was put through rehabilitation. At 19 she was subjected to daily interrogations for six months.
"One afternoon Alice swallowed a tin of paint thinner and jumped from a 15ft roof.
"The whole thing was hushed up. Alice is now crippled."
Despite the risks, John told his superiors he needed to visit a sick relative in Ireland, then he fled to a hotel in Birmingham where he hid for a week.
He says officers were sent after him and even staked out relatives.
In a bid to lure them away he made sure he was sighted near the Birmingham Scientology office.
Then he fled to Dublin when he knew the officers had been recalled to England.
John is now rebuilding his life in his native Co Cork. He says: "I gained nothing. I still bear the scars of my time in the church.
"But I'm now studying for an arts degree, getting to know my family and putting the past behind me."
