Official guidance to stop therapists offering gay people treatment to "change" their sexuality was called for today by the National Secular Society.

It made the move in response to a decision by the American Psychological Association to discourage its 150,000 members from making such claims.

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In a letter to the Royal College of Psychiatrists, president of the NSS Terry Sanderson wrote: "We would like to suggest that the Royal College of Psychiatrists considers issuing an advisory to its own members that they should not offer to provide these therapies nor suggest that people seek them out elsewhere - particularly from religious groups.

"Enough research has now been done in this area to show that the therapies are not only ineffective, but often lead on to further problems."

The NSS cited a survey by University College London of 1,300 therapists earlier this year which found that a minority had tried to change patients' sexuality.

Mr Sanderson said: "The idea of curing homosexuals comes these days mostly from evangelical Christian groups who are convinced that the Bible condemns homosexual practice.

"Telling people that they can be "cured" of their sexual orientation suggests that it is an illness, and to suggest that they can be "converted" to heterosexuality raises hopes that will eventually be dashed, possibly leading to depression and suicidal impulses."

The Royal College of Psychiatrists said it took the call "very seriously".

A spokeswoman said: "The college takes very seriously the call by the National Secular Society to issue broader guidance to our members and will look into the issue further."

Earlier this year the college said it shared American concerns over these practices, and that lesbian, gay and bisexual people had the right to be protected from potentially damaging therapies.