Billy Leung is not a murderer, a drug trafficker or a criminal of any kind. But in the eyes of Hong Kong law, this 20-year-old employee of the humanitarian group Médecins Sans Frontières might as well be.

His offence? Mr Leung is homosexual in a city that considers consensual sex between two men, where one or both are under the age of 21, a crime punishable by a maximum penalty of life imprisonment.