Submissions to the Church of England's Working Group on Human Sexuality by the Royal College of Psychiatrists (RCG) either ignored or misrepresented scientific research, a letter to bishops claims.

The letter was sent by Dr Peter May to members of the Church of England General Synod today as bishops met to discuss the Pilling Report on human sexuality. 

The Pilling Report was compiled by the Working Group and makes 18 recommendations to the Church of England on the question of human sexuality.

These include the recommendation that the Church of England "warmly welcomes and affirms the presence and ministry within the church of gay and lesbian people both lay and ordained". Clergy should also be allowed to offer prayers for same-sex couples, the report suggests.

"There has been a serious failure to address the known science of human sexuality," said Dr May, a retired GP and member of the Royal College of General Practitioners, and a former member of the General Synod.

The Church of England is currently going through a process of examining its position on homosexuality. The Working Group was established by the House of Bishops and led by Sir Joseph Pilling, a retired senior British civil servant with strong charity connections.

Dr May asserted that the RCG's submissions to the Pilling Commission overlooked aspects of existing scientific evidence on human sexuality and that there were inconsistencies within the RCP's own judgements.

The letter firstly points to differences between the RCP's 2007 submission to the Church of England Listening Exercise on Human Sexuality and its 2012 submission to the Pilling Commission.

In 2007, the RCP stated: "It would appear that sexual orientation is biological in nature, determined by a complex interplay of genetic factors and the early uterine environment. Sexual orientation is therefore not a choice."

But in 2012, the RCP is quoted as saying that homosexuality is "determined by genetic factors and/or the early uterine environment".

The letter explains that the 2007 position "implies that genetic and hormonal influences are working together", while the 2012 position "logically allows that orientation may be caused entirely by genes or entirely by hormones".

"Conversely, it may have nothing to do with genes or nothing to do with hormones," he said.

"The College thereby admits that there is no compelling evidence to say it is genetic or hormonal. Where then is the evidence that orientation is biological in nature?"

Dr May went on to question why the RCP failed to mention studies on twins in its submissions, which suggest that even where one identical twin is gay, there is an 89% chance the other will not be.

He argues that while there may be genetic factors involved in homosexuality, they cannot be considered absolutely determinative.

"As [twins share] essentially similar genes and intrauterine environments, this strongly suggests the importance of later postnatal, non-biological causes, such as events or choices, in determining sexual orientation," he writes.

While the RCP claims that there is no substantive evidence that the nature of parenting or early childhood experiences play any role in the formation of a person's sexual orientation, Dr May says this ignores a 2006 study into two million Danes, published in the Archives of Sexual Behaviour, which concluded that "childhood family experiences are important determinants of heterosexual and homosexual marriage decisions in adulthood".

"The College appears to have locked itself into a 'born gay' ideology by ignoring the evidence to the contrary," Dr May said.

The letter questioned the RCP's assertion that discrimination in society and possible rejection by friends and family were behind high rates of homosexual suicides. Dr May pointed to Denmark, where between 1990 and 2001 suicide rates among men in civil partnerships were eight times higher than among married heterosexual men, despite civil partnerships being legalised in 1989.

Three studies taken by the RCP to support the notion that homosexuality and mental health problems are correlated mainly due to societal intolerance are less than definitive, Dr May goes on to argue.

One study claimed that the "the precise causal mechanism at this point remains unknown. Therefore studies are needed...to evaluate the relative salience of social stigmatization and lifestyle factors."

Another, which was conducted by Dr Michael King, the author of the RCP's submission to the Pilling Commission, said that "gay men and lesbians may have lifestyles that make them vulnerable to psychological disorder".

However, in his submission statement to the Church of England, he said "discrimination in society...means that some LGB people experience a greater than expected prevalence of mental health and substance misuse problems".

The third study says "many people will conclude that widespread prejudice against homosexual people causes them to be unhappy or mentally ill".

"[This view] would be premature however and should be discouraged. In fact a number of potential interpretations need to be considered," the study says.

The letter also criticises the RCP's attitudes towards therapy addressing unwanted same sex attraction - or reparative therapy - and suggested such attitudes were based upon assumptions that sexual orientation is innate.

"There is considerable evidence that sexual orientation is fluid, and can change over the course of life with or without therapy," he said.

"This is particularly well documented among young people and also among women. Furthermore, it is now recognised that more people are bisexual than homosexual, their orientation being essentially fluid.

"Secondly, evidence of harm harks back to 40-50 years ago, when electric shock and drug therapies were being used to 'cure' homosexuality. This has nothing at all to do with modern psychotherapeutic methods aimed at ameliorating intrusive desires."

The letter concludes by noting that the UK Council of Psychotherapy has failed to respond to requests for peer-reviewed studies linking reparative therapies and harm.

A more detailed form of this letter had been compiled into a booklet entitled "Beyond Critique – When Ideology Replaces Science".

The booklet was sent to Sir Joseph Pilling, ahead of the next meeting of the General Synod in February, where the Pilling Report is due to be discussed.

The Pilling report in its current form is sceptical of the notion that individuals are "born gay", but does not rule it out completely.

Page 62 and section 203 of the Pilling Report says: "It is important to note that it is a simplification of the scientific evidence to say that any one individual is 'born gay'. It seems likely that there are people who for biological reasons have a greater propensity to same sex attraction, but whether they will become involved in same sex sexual relationships or identify as gay or lesbian will be shaped by familial, social and personal factors. To adapt the old feminist slogan 'biology is not destiny."