Britain’s largest professional body of psychotherapists has warned its members against attempting to “convert” gay people, after discovering practitioners were still offering the “treatment”.

The warning comes after California’s Governor Jerry Brown signed a state bill to outlaw the practice for teenagers last weekend.

Mr Brown said gay conversion therapy had “no basis in science or medicine”.

The Telegraph reports that the British Association for Counselling and Psychotherapy (BACP) has now notified its 30,000 members of the formal change in policy, advising them that being gay is not a “mental disorder”.

In a letter sent to its members the BACP said it opposed “any psychological treatment such as ‘reparative’ or ‘conversion’ therapy which is based upon the assumption that homosexuality is a mental disorder, or based on the premise that the client/patient should change his/her sexuality.”

In July 2011, the Christian therapist was found guilty of malpractice by the BACP, after she was shown in 2010 to be providing gay conversion treatments following an undercover investigation by the journalist Patrick Strudwick.

A spokesman for the BACP said that Ms Pilkington’s case highlighted the need for tighter rules.

The practice of gay conversation therapy, which is largely supported by the fringe parts of the Christian evangelical movement, remains a global problem.

Last month, an Australian doctor was banned from practicing medicine after he prescribed a teenager with a chemical castration drug for use as a ‘gay cure’.