The London Oratory in Hammersmith, west London, is believed to be the only state-funded school in England that defied a government ban on using interviews to determine which pupils to admit.
The move was opposed by a local primary school, Peterborough, which claimed the interviews favoured articulate, middle-class parents. The school objected to the Office of the Schools Adjudicator; it referred the decision to Ms Kelly.
John McIntosh, its headmaster, said the interviews were necessary to determine the religious commitment of the parents to the school's ethos. It is a Catholic school.
The school insists it will not use the interviews just to admit Catholics - but wants to determine the religious commitment of families from other faiths and does not want just to rely on the recommendation of a priest or vicar.
In her ruling, sent to the primary school and local education authority, Ms Kelly accepts the interviews are necessary to determine this. Her decision is bound to spark fury from parents opposed to covert selection who would prefer an independent ruling. They are likely to point out that not only is Ms Kelly a cabinet colleague of Mr Blair but she is also a committed Catholic who came under fire for her links to Opus Dei, a conservative Catholic group.
n Barton grammar school in Canterbury, Kent, is set to become the first state-funded school to abandon A-levels in favour of the International Baccalaureate. Pupils will study seven compulsory subjects instead of the traditional three A-levels.