The Government introduced legislation in 1998 aimed at allowing state-maintained faith schools - notably those run by Anglican and Catholic churches - special dispensation to employ staff of a particular faith.
The school standards and framework Act ensured that they did not fall foul of 2003 employment regulations that made it illegal to discriminate against people on grounds of religious belief. The safeguards were later extended to fee-paying schools under the 2003 religious character of schools regulations.
King's academy and another school sponsored by the charity, Emmanuel city technology college, were registered under the regulations in January 2004, granted following an inspection by officials at the Department for Education and Skills.
Trinity was registered in October last year. The Oasis Trust's academy in Enfield, north London, which will open in September 2007, also won the status last October and two United Learning Trust academies - in Lambeth and Northampton - were registered in July 2004.
Two academies sponsored by the Church of England - Grieg academy, in north London, and the Samworth academy, to open in Leicester next year - also have the status, as does the Catholic-sponsored St Paul's academy in Greenwich, London.