A simmering conflict at the Church of Scientology has been made spectacularly public after a former member of the organisation's clergy circulated a letter raising severe criticisms of both the management style and financial policies of its current leader, David Miscavige.

Debbie Cook's email, which was sent to 12,000 fellow Scientologists shortly after midnight on New Year's Day, alleges that Mr Miscavige has adopted a dictatorial leadership style which is at odds with the doctrines laid down by the church's founder, the science fiction author, L Ron Hubbard.

She further claims that, since succeeding Hubbard after his death in 1986, Mr Miscavige has become obsessed with fundraising. His regime is now "hoarding" a cash reserve of more than a billion dollars, she claims, and has spent tens of millions more on a portfolio of large, "posh" buildings which largely sit empty.

Ms Cook's criticisms strike a chord with many disaffected recent defectors from the church. But her highly respected status within the usually secretive world of Scientology may also give them weight among more active members.

The email, headlined "Keep Scientology Working" and littered with jargon, argues that many of the policies pursued Mr Miscavige are in direct conflict to the principles laid down by Hubbard when he created the movement in the 1960s and 1970s. In particular, she claims that "extreme" fundraising activities are now being "driven from within the very highest echelons of the Scientology structure", in a way that is at odds with the organisation's founding scriptures.

Although many current members have donated vast portions of their net worth to the church, Ms Cook claims that Hubbard never endorsed individual donations of over $75 for lifetime membership. The church's founder also "never authorised the purchase of opulent buildings" by the leadership, she argues. Instead, he believed that all money raised by the organisation should immediately be used to spread its message.

Now aged 50 and living in Texas, Ms Cook was for three decades a member of "Sea Org," Scientology's equivalent of the clergy. Between 1999 and 2006, she was Sea Org's top representative at the church's global headquarters in Clearwater, Florida.

Later, she moved up to its ranks of management, and between 2006 and 2008 was based at its offices in California. It was in that capacity that Ms Cook directly witnessed Mr Miscavige's management style. She now argues that it subverts the checks deliberately established by Hubbard to prevent any one individual from gaining complete control of the church. In 2008, she left the church's payroll to start an internet firm with her husband. But she remained an active Scientologist and claims to remain "completely dedicated" to its beliefs.

Following her email, several former "friends" used Ms Cook's Facebook page to announce that they were "reporting" her to Scientology's "ethics" department.

A church spokesman said: "Ms Cook's opinions reflect a small, ignorant and unenlightened view of the world today. They are not shared by thousands of Scientologists who are overjoyed by our 27 new churches and what they mean to the communities they serve."

Debbie Cook's message: The key quotes

* "David Miscavige has now become the 'leader' of the Scientology religion... There never was supposed to be a 'leader' other than [L Ron Hubbard] himself as the goal maker for our group."

* "... There is no question that this new age of continuous fundraising is not our finest moment."