The Independent has already disclosed how Ms Kelly gave the green light to the London Oratory, which is attended by Tony Blair's eldest three children, to carry on interviewing parents - in breach of a government code on school admissions. The interviews are to determine their commitment to the Catholic faith in order to help the school decide which pupils to admit.
But it has emerged that Ms Kelly refused permission to Gunnersbury Roman Catholic School, in Hounslow - the neighbouring borough - to do the same thing.
Bob Garnett, the vice-president of Confed, the association that represents senior education officers, said last night: "Is there one law for the middle classes and those who know Tony Blair and another law for the rest?"
Mr Garnett, who is also director of lifelong learning, leisure and cultural services in Hounslow, said that the authority was "very pleased" with the decision over Gunnersbury because it had objected to the interview process.
"I don't think anybody should be interviewed," he said. "The priest is the right person to determine a person's faith." However, he said that the two decisions taken together left government policy unclear.
Both are boys' schools for 11- to 18-year-olds with girls in the sixth form and are massively oversubscribed. They both have above- average exam results.
The 1,300-plus pupil London Oratory, though, has, according to its latest report from Ofsted, just 7.9 per cent of pupils on free school meals - compared with 22 per cent at Gunnersbury.
Both have about one in three pupils whose first language is not English - and the performance of pupils upon intake is above the national average.
In her letter outlining her decision on Gunnersbury, Ms Kelly makes it clear that faith schools have been told interviewing should not play a part in the admissions process and they should find another way of gaining the information they need. That advice was sent out to schools only last month.
"The school's admissions arrangements should not include interviewing, as it is unclear to parents; insufficiently objective to form part of the admission process for a state-maintained school; and, because of this lack of clarity and objectivity, potentially unfair in how places are allocated," she added.
"Furthermore, there appears to be no need for it as the relevant criteria can be established by other means." However, in her letter about the London Oratory decision, she said she had noted the governing body's evidence "about the unique nature of the school: its long tradition of admitting pupils on the basis of the degree of religious adherence and practice; and its tradition of admitting pupils across London". She said its interviewing arrangements were "clear, fair and objective".
The governors of the London Oratory had stressed in evidence that they admitted pupils from more than 400 parishes and primary schools, 40 local education authorities and four dioceses.
As a result, the interviews were considered by the school to be "the most useful and practical means by which to determine the religious practice and commitment of candidates."Reuse content