Education Secretary Estelle Morris has revised the system for checking staff backgrounds, amid chaos to the new school year caused by problems at the Criminal Records Bureau.

The Government announced last night that teachers and teaching assistants who have not been cleared by the CRB will be allowed to work in schools at the discretion of headteachers.

Ms Morris said the decision was taken because the CRB was not processing their applications quickly enough.

She said all staff would still have undergone checks against List 99, the secret dossier of people convicted or suspected of child abuse.

"I apologise for any part I have had in bringing this about," Ms Morris said. "I am a customer in this, I am a client, I am a client of the CRB who are meant to do the checking.

"There is no doubt that as a customer I am a very dissatisfied customer and I will want to be asking questions."

The Education Secretary said: "What I have decided is to revert to the checking system that was in place in schools at the end of the summer term."

John Dunford, general secretary of the Secondary Heads Association, welcomed Ms Morris's decision.

He said: "I'm still not apportioning blame - I think the blame is shared between the agency and the Government in a situation which was entirely predictable and avoidable."

Ms Morris said: "I do regret a messy start to term. As a teacher, you want a crisp start."