It was the autobiography that gave hope to hundreds of thousands and warmed the hearts of Christians.

Chronicling how a convicted criminal and martial arts fighter found redemption through God, Taming the Tiger had more than 1.5m copies distributed around the world while its author, Tony Anthony, become a sought-after speaker in schools and churches.

In the book, which carries the strapline "From the Depths of Hell to the Heights of Glory", Anthony explains how he was taken to China by his grandfather, a kung fu grand master, and trained to become a martial arts champion. He then moved to Cyprus, where he became a bodyguard to businessmen, gangsters and diplomats. "In the line of duty as a bodyguard, I killed people," Anthony would tell church audiences. "I have broken more arms and legs than I care to remember." Later he recounted how he found God while in prison in Nicosia after being convicted of theft.

The book was a phenomenon. It was translated into 25 languages and won the Christian Booksellers' Convention Award in 2005.

But now, following a sustained internet campaign by a group of Christians who doubted Anthony's claims almost from the start, it appears that little of the book is true.

Anthony, who founded his own organisation, Avanti Ministries, was the star speaker during the Evangelical Alliance-backed Global Day of Prayer in 2010, attended by the mayor of London, Boris Johnson.

After an independent investigation, a panel appointed by the alliance has concluded that Anthony had, at best, a sketchy relationship with the truth. In a statement on its website the alliance acknowledges that "large sections of the book Taming the Tiger, and associated materials, which claim to tell the true story of Tony Anthony's life, do not do so".

It continues: "Both the Evangelical Alliance and Avanti Ministries take serious note of the findings of the report and, as a result, Avanti has concluded that it is not appropriate to continue to support Taming the Tiger." The alliance launched its investigation after a director of Avanti, Mike Hancock, resigned. An online blog, Crosswire, explained how Hancock had become sceptical after demanding proof of Anthony's claims.

"I understood that I had a moral and ethical responsibility to ensure that his story could be thoroughly verified," Hancock told the blog. "I was unable to persuade my fellow directors of the need to do this. I therefore resigned from Avanti and pursued the search for truth with other like-minded Christians," he said.

Anthony claimed to be a three times world kung fu champion and tried to deflect suspicions that he had embellished his past by claiming that the competitions were so specialised they were not known to outsiders. But it emerged that some of the material was copied from a martial arts website. One passage was lifted from a book about Bruce Lee.

The Evangelical Alliance acknowledges: "The complaint focused on the truthfulness of the story told in Tony's bestselling book Taming the Tiger. It was alleged that Tony had never lived in China as a child, had never been involved in kung fu as a world champion and had never worked in close protection. Having considered the extensive evidence presented to us, much of which is now in the public domain, we were convinced that this information could not be ignored."

Critics of Anthony, who raised suspicions that many of his claims were untrue as far back as 2005, are now asking why it took the alliance until last year to launch an investigation.

In his book Anthony explains how in 2000 he thought he had hit a "small deer or fox" after his car hit Elizabeth Bracewell, 39, the sister of the former England footballer, Paul Bracewell. She died as a result of her injuries.

During his trial after the death, Anthony, from Southend-on-Sea, was described by the judge as a "devious and manipulative man" who had "deliberately embroidered his story" to throw police off the scent. He was given a 15-month sentence after admitting perverting the course of justice.

The Evangelical Alliance has been keen to show forgiveness towards Anthony. It explains: "The alliance and Avanti Ministries are deeply saddened by the findings of the panel. However, they recognise the good work that Avanti and Tony Anthony have done over the years around the world and the impact this will have on the charity and specifically Tony and his family."

Attempts to reach Anthony through Avanti's email address were unsuccessful. Avanti's website states: "After much prayer, Avanti have decided the time has come to close its ministries."

In a statement, Anthony's publisher, Authentic Media, said that it was withdrawing Taming the Tiger, a follow-up book, Cry of the Tiger, and a related DVD.

It said: "Tony strongly defends his story – though he acknowledges that the recent information that he has received about his early life requires him to update and clarify his story."

• This article was amended on 2 August 2013. The original suggested that Tony Anthony was "championed" by the Evangelical Alliance. The Alliance has issued this statement: "Tony Anthony has never been employed by the Evangelical Alliance, represented us, or spoken on our behalf. Revelations that have come to light about the authenticity of Tony Anthony's book have been reported by us because of the many concerns raised by evangelical Christians, not because we represent Tony Anthony. We recommended an independent investigation which was subsequently carried out."

