The man had been explicitly cleared to work in schools by ministers and officials reporting to Ruth Kelly, the previous education secretary. But Alan Johnson told Parliament this week that the man had been visited by police and had now been barred.
The man was one of 56 registered sex offenders who had been similarly cleared to work in schools. The other 55 have been reassessed by police and ministers as posing no threat to children. Mr Johnson did not identify the man.
The Norwich PE teacher at the centre of a political furore last year was a registered sex offender who was cleared to work with children by a former education minister, Kim Howells. It is not known whether he is the man barred. Paul Reeve had been cautioned by police and placed on the Sex Offenders Register for accessing child pornography websites.
Mr Johnson also barred 12 offenders who had previously been "partially barred", on the Government's confidential List 99, from working with children.
One partially barred offender, whose case became public last year, was Keith Hudson, a Sussex teacher convicted of possessing indecent images of young boys. He was cleared by former education secretary Estelle Morris to work in an all-girls school. Again, it is not known whether he is one of the 12 now barred.
Last week, The TES reported the suspension of Darren Smith, a Leeds technology teacher who had been arrested for suspected gross indecency with a child.
He was suspended in January 2004 for concealing his police record. His case was reported to the Department for Education and Skills misconduct unit, but he was still able to get supply work in six Leeds schools.
Dr Stuart Wilson, the headteacher of a seventh school, Featherstone technology college in Wakefield, refused Smith a job after checking his references.
He told The TES this week that schools needed to be vigilant in their checks: "It is not enough to rely on List 99 and the Criminal Records Bureau," he said.
New rules which came into force this week mean any adult convicted or cautioned for a sex offence should be be automatically included in List 99.
From September next year, a new vetting and barring regime will continuously monitor about 10 million adults who have sought to work with children, in case they are arrested or charged with offences.