The admission came as police and social workers investigated claims that a former chaplain sexually abused pupils at the London Oratory, a leading Catholic state school attended by two of the Prime Minister's sons.
The priest, Father David Martin, died two years ago, aged 44, of an Aids related illness. His alleged victims fear they may also have contracted HIV.
Father Martin was ordained in 1994 and was the school's chaplain for four terms till July 1998.
The inquiry was triggered by a letter to Hammersmith and Fulham social serices last week from a boy claiming to be at the school, who has still not been identified.
ChildLine, the telephone helpline, had also been contacted about alleged abuse at the school and a number of people in the Westminster diocese had received anonymous letters.
Schools are required by law to check if teachers, governors and other volunteers are on List 99, the official register of people deemed unfit to work with children. A DFEE spokesman added: "If governors or others (including chaplains) have regular substantial unsupervised access to children, a criminal record check should also be sought."
He refused to say if Father Martin was on List 99, as such information was never disclosed. He alo refused to comment on whether the priest had a criminal record.
Tom Horwood, of the Catholic media office, said new priests were asked to declare any convictions. But there was no national policy of police checks, though some were carried out on an ad hoc basis. He said: "Some dioceses have approached police about checks ... Some forces have said fine, others have said it will cost a lot ... some dioceses have contributed to the costs. One police force said it didn't consider priests to be a high risk, and that checks were not worth doing."
Lord Nolan, the former public standards watchdog, is leading a review of the church's child protection arrangements, and should produce an interim report soon after Easter. His review follows a string of high-profile abuse cases involving Catholic priests.
From next year, employers can vet job applicants through the new criminal records bureau. But a Home Office spokesman said there was nothing to force the church to join the scheme.
Father Ignatius Harrison, chair of the governors, said the Fathers of the London Oratory - an order with close links to the school which appointed Father Martin - were co-operating fully with the authorities.
A Hammersmith education authority spokeswoman said she understood the Oratory Fathers now carried out police checks on priests, but had not at the time of the alleged abuse. Father Martin had not been vetted. She said it was too early to say how many boys might be involved.