At least two teachers, who had committed offences on a special government list of 42 crimes against children which should have resulted in automatic, permanent bans from teaching, were allowed back into schools.
Keith Hudson, who was convicted of importing indecent images of young boys, and Mr "H", convicted of molesting a 12-year-old, among those named in the current political crisis, were cleared to teach again.
The TES can also reveal that the Department for Education and Skills has gone against its own guidance by referring teachers who have committed crimes relating to child welfare to the General Teaching Council.
The DfES has been referring cases such as assaults on pupils, serious violence and sexual offences to the GTC when its guidance recommends that the Education Secretary should examine them. The GTC is taking a year to hear conduct cases and has admitted that a sharp rise in referrals is causing the delays.
The inconsistencies in applying the rules may explain why some of the teachers referred to the DfES by local authorities have not been put on List 99, which would bar them from working in schools.
Essex council has complained that since 1992, only half of the teachers it referred to the DfES were included on the list.
The revelations will add to pressure on Ruth Kelly, Education Secretary, who has been fighting for her political survival.
The Government has suffered nearly a fortnight of criticism as a growing list has emerged of convicted sex offenders who have been allowed to teach.
Ms Kelly was due to announce yesterday that she was accelerating plans to introduce vetting procedures, which civil servants have been developing since 2004 in response to Sir Michael Bichard's inquiry into the Soham murders.
The Education Secretary was expected to say that ministers would not be allowed to make decisions themselves on whether teachers should be barred and would instead pass responsibility to an independent panel of experts.
The changes are aimed at addressing several of the problems which the Government has publicly acknowledged, including inconsistencies between the many registers listing adults unsuitable to work with children.
The DfES guidance on child protection lists 42 sexual and violent crimes against children which should lead to automatic, permanent bans.
These offences range from murdering, raping, or indecently assaulting a child to possessing indecent pictures of children and causing a young person under-16 to witness sex.
Teachers' unions said the vetting system was a muddle which should have been fixed sooner.
TES Cymru, the paper's Welsh edition, has revealed that large numbers of school inspectors in Wales have not had full Criminal Record Bureau checks, although they were vetted against List 99.
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