Ministers have ignored their own rules for keeping teachers who are guilty of crimes against children out of the classroom.
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.
The Department for Education and Skills has also gone against its own guidance by referring teachers who have committed crimes relating to child welfare to the General Teaching Council for England, which is taking a year to hear conduct cases. In Wales, such cases are referred to the DfES, not the GTCW.
The revelation will add to pressure on Ruth Kelly, Education Secretary, who has been fighting for her political survival after it emerged that convicted sex offenders have been allowed to teach.
Ms Kelly was due to announce yesterday that she was accelerating plans to introduce new vetting procedures, developed in response to Sir Michael Bichard's inquiry into the Soham murders.
She was also expected to say that an independent panel of experts, rather than ministers, would in future decide whether teachers should be barred.
The changes aim to address inconsistencies between the many registers listing adults unsuitable to work with children.
But ministers have been letting teachers back into schools who have been convicted of offences on a DfES list, and who should have been automatically banned. Keith Hudson, who was convicted of importing indecent images of young boys, and Mr "H", convicted of molesting a 12-year-old, were allowed to teach again.
Meanwhile, it emerged this week in an Estyn newsletter that a "large number" of inspectors have been working in Welsh schools without being checked by the Criminal Records Bureau (CRB).
The affected inspectors, employed by private companies, joined under contract before the CRB was established in March 2002.
Estyn says they were subject to the equivalent of the CRB's "standard disclosure", including checks against List 99. It now has a new policy requiring all independent inspectors to undergo an "enhanced" CRB clearance to carry out inspections from September.
The enhanced checks, which cover details of convictions, acquittals and other information on police records, will then have to be carried out every three years.
A spokesperson said Estyn was introducing more checking than was required of school inspectors. But Iwan Guy, acting director of the National Association of Head Teachers Cymru, said: "I would have thought all school inspection teams were subject to the check."
Geraint Davies, secretary of teachers' union NASUWT Cymru, said: "Anybody in direct contact with children must be CRB checked. I'm surprised."
Education and lifelong learning minister Jane Davidson told Assembly members there were no List 99 teachers registered with the GTCW to work in Welsh schools - but could not say if others registered elsewhere in the UK were working in Wales.