Mitt Romney, the front runner in the race for the Republican Presidential nomination for the White House, is a devout Mormon, but his cousin, Park Romney, also in the past a committed member of the church, now denounces it as a cult.

"I became convinced that it's a fraud," Park Romney told the BBC, explaining his reason for leaving the Mormon fold.

The two visions of Mormonism the Romney cousins present could not be more starkly opposed.

Park Romney, 56, is a former Mormon high priest, who turned against the church.

On the stump Mitt Romney, 65, has avoided mentioning Mormonism, instead talking generally about his faith, but he has been an active lifelong member of the church.

"If that is what they believe, it's probably a good thing they leave, because we're not a cult Jeffrey Holland, Mormon Church Elder

He was a Mormon missionary to France in the 1960s, studied at the almost-exclusively Mormon Brigham Young university and rose to become first bishop, then "Stake President" (diocesan leader) in his home state of Massachusetts.

He led Sunday services, ran Bible classes for children and looked after a 4,000-strong congregation in Boston for five years in the 1980s.

Like all Mormons, he is expected to give 10% of his annual income - no-one knows how much he is worth, but it is estimated at anywhere from $150 million to $1 billion - to the Church and not drink tea, coffee or alcohol.

Committed Mormons wear special under-garments, and Romney is believed to follow this tenet of his faith too.

Park Romney's criticisms of the church are fundamental.

Along with other ex-Mormons, he questions founder Joseph Smith's prophecies - for example Smith's translation of an Egyptian scroll, part of the Mormon book of Abraham, which Egyptologists say is a fraud.

The Mormon faith Official name is Church of Jesus Christ of Latter-Day Saints

Founded in the 1820s in New York State before moving to Utah in 1860

Mormons believe their founder Joseph Smith found golden scripture plates buried by an angel

The church is estimated to have 14 million followers and to be worth $30bn (£18.9bn)

A recent poll said one in four Americans would be less likely to vote for a Mormon candidate BBC Religion: Mormonism Is the US ready for a Mormon president?

"There's compelling evidence that the Mormon Church leaders knowingly and wilfully misrepresent the historical truth of their origins and of the Church for the purpose of deceiving their members into a state of mind that renders them exploitable," says Park.

Such accusations are rarely heard in the US, a nation founded on the principle of freedom of religion.

"It's not something you're supposed to talk about," says Prof Robert Putnam of Harvard Kennedy School.

"Whenever the issue of Romney's Mormonism has come to the surface, there's been lots of condemnation across the political spectrum for raising the issue of his religion," says Putnam.

"I'm not saying it's not relevant, but it's not talked about in polite company."

Mitt Romney's biographer, Scott Helman, agrees.

Find out more The Mormon Candidateis part of the latest series of This World, broadcast on Tuesday 27 March at 19:00 BST on BBC Two

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"There are plenty of ways in which people try to cause alarm among some voters over it, but it's not something you're allowed to say explicitly," he says.

"But a certain function of reminding voters who might have some predisposed notion about Mormonism that maybe it is strange, maybe it's weird."

Ex-Mormons tend to be the church's most outspoken critics.

One thing that particularly agitates them is "shunning" - allegations that former church members are denied access to family members who remain in the church.

Park claims this has happened to him.

"I am alienated from my family," he told the BBC.

"Their doctrine, their protocol and their culture as enforced by bishops encourages the families to disassociate themselves from the apostate."

Image caption Mormon headquarters are in Salt Lake City, Utah

Mormon Church elder Jeffrey Holland denies shunning occurs.

"We don't use that word and we don't know that practice.

"If I had a son or a daughter who left the Church or was alienated or had a problem, I can tell you I would not cut that child out of family life," he states.

The Mormon Church maintains that it does a great deal of good. Its leaders say they have given more than $1bn in aid around the world since 1985.

The allegation that the Church is a cult, made by Park Romney and other ex-Mormons, is denied by Elder Holland.

"If that is what they believe, it's probably a good thing they leave, because we're not a cult.

"I have chosen this church because of the faith that I feel and the inspiration that comes, but if people want to call us a cult, you can call us a cult," Elder Holland says from behind his desk.

"But we are 14 million and growing."