She made her claims in a 22-page paper submitted at the Committee Stage of the Marriage (Same Sex Couples) Bill.

It contained a detailed analysis of marriage trends in Sweden, Norway, Denmark, Spain, Belgium, Canada and some U.S. states were gay marriage has been legalised.

"From what we know about demographic trends, it is preposterous to argue that people suddenly somehow embrace marriage and slow or reverse its decline because homosexuals can have it," Dr Morgan said.

"We can be certain that same sex marriage will do no such thing as encourage stable marriage whether for heterosexuals and/or homosexuals. Marriage in Scandinavia, Spain, Netherlands and elsewhere is in deep decline."

She continued: "Same sex marriage is both an effect and a cause of the evisceration of marriage - especially the separation between this and parenthood."

Dr Morgan explained that gay marriage became conceivable only in those countries where marriage was already in crisis because of soaring "out-of-wedlock births and cohabitation rates" and invariably made such problems worse.

"If marriage is only about couple relationships, and is not intrinsically connected to parenthood, why not give the leavings to homosexuals?," she asked.

"As marriage is redefined to accommodate same-sex couples, this reinforces the irrelevance of marriage to parenthood," she said.

"Elsewhere, same sex marriage is an instigator for the casualisation of heterosexual unions and separation of marriage and parenthood."

She added: "Same sex marriage is more a terminus for marriage or ultimate act of dissolution, rather than a force for revival."

The Coalition Government has consistently argued that David Cameron's controversial gay marriage Bill will have the effect of strengthening all marriages by opening it up to same-sex couples.

Last year the Home Secretary, Teresa May, told The Daily Telegraph that "homosexuals will be missionaries to the wider society and make it (marriage) 'stronger'".

But the research by Dr Morgan, the respected family policy analyst who coined the phrase "marriage lite" to describe cohabitation, provides hard evidence that in fact the opposite is likely to happen.

Spain in particular, she said, saw a "precipitous" downward acceleration in the numbers of all marriages by a 15,000 a year in first three years that followed the legalisation of same-sex marriage by the Socialist government in 2005.

The rate of decline later more than doubled to 34,000 fewer marriages a year in between 2008 and 2010.

Dr Morgan also produced evidence to show that heterosexual marriages were less stable in those countries where same-sex marriage had been introduced because they were expected to conform to the values of gay couples whose unions were often open, rather than exclusive, and far more likely to break down.

Cohabiting gay couples were 12 times more likely to separate that married heterosexual couples, she said.

Dr Morgan also predicted the widespread victimisation of individuals and institutions who dared to resist the redefinition of marriage.

"Some clearly hope that compulsion to perform same sex weddings will sever Church and state and further push Christianity out of the public arena and, therefore, consciousness," she said.

"Undermined and stigmatised for their unreasonableness and prejudice, the moral authority of religious institutions will further retreat in favour of a narrow secular ideology, particularly as sexual behaviour at odds with traditional norms is further encouraged and advanced."

The Prime Minister has faced intense criticism from the mainstream Churches and within his own Conservative Party for fast-tracking gay marriage through Parliament when there was no mandate or demand for it.

His preoccupation with the issue has been blamed for the collapse of grass roots activism and partly for the recent electoral successes of UKIP, which pushed the Tories into third place at the Eastleigh by-election last week.

END