American motorists will be subjected to a new motorway billboard declaring that “nobody is born gay”.

The advert, on Interstate 95 in Richmond, Virginia, was paid for by a US group that claims it is possible to change the gender of person someone is sexually attracted to.

The group, which calls itself ‘Parents and Friends of Ex-Gays & Gays’ (PFOX) claims that studies on twins claim that “nobody is born gay”.

In response to an upsurge in claims by US religious groups that they can stop a person being gay, the American Psychological Association said such approaches had absolutely no foundation in science.

“Some religion-based organizations … have invested significant resources in the promotion of sexual orientation conversion therapy and ex-gay ministries to educators and young people in conferences, in advertising, and in the media,” it said in a pamphlet outlining its position.

“The most important fact about these ‘therapies’ is that they are based on a view of homosexuality that has been rejected by all the major mental health professions.”

In a statement, group responsible for the billboard said: "We find it interesting that the attacks against the billboard and ex-gay community have nothing to do with the facts.”

The group has hired US PR company Hamilton Strategies, apparently in order to gain media attention. The company that agreed to take the billboard is called Lamar Advertising, the group said.

Last month John Smid, the former leader of a similar prominent US “ex-gay” group finally married his male lover after admitting that it was impossible to deny one’s sexuality.

“I’ve believed in faith that something was going to happen, and it never did, and so at my age, right now in my life, I don’t have that many good years left in me, and I can’t live like this for the rest of my life, so I said no, I’m not willing to keep pushing after something that’s not going to happen," he said at the time.

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Many influential US religious groups regard being attracted to people of the same sex as undesirable and campaign against equal marriage rights.

Fifteen states in the county have explicit bans on same-sex marriage as a result of political support for such groups.

A similar advert on buses in London was banned by the Mayor in 2012 after it was branded "sad".