Britain's biggest professional body for psychotherapists has instructed members that it is unethical for them to attempt to "convert" gay people to being heterosexual, formalising a policy change long demanded by rights groups.

The British Association for Counselling and Psychotherapy has written to its near-30,000 members to inform them of the new guidelines. The letter says the BACP "opposes 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". The body adds that it recognises World Health Organisation policy that says such therapies can cause severe harm to an individual's mental and physical health.