Ex-Tory leader Michael Howard has called for Education Secretary Ruth Kelly to quit over the row about the employment of sex offenders in schools.
Mr Howard, in the News Of The World, said Ms Kelly should not be in her job if she "doesn't know what's going on".
The Department for Education launched a review after it emerged that a convicted sex offender was working in a Bournemouth school since September.
William Gibson was convicted of indecently assaulting a child in 1980.
He was employed as a supply teacher at Portchester School despite having been removed from three previous schools after his record was discovered.
It has emerged that, since his conviction, Gibson worked at two schools in South Tyneside and one in neighbouring County Durham from 2003 to 2005.
Ms Kelly has faced a barrage of criticism since it emerged last Sunday that her department had cleared a PE teacher to work at a Norwich school even though he had been cautioned for accessing child pornography.
The pressure intensified as news emerged of Gibson's employment, as well as that of Keith Hudson, from Sussex, who was given permission by then Education Secretary Estelle Morris in 2001 to teach in all-girl schools, despite a conviction for possessing indecent images of boys in 1996.
Mr Howard, who introduced the sex offenders' register while he was home secretary, said the news that people on the list had been allowed to work in schools was "a scandal".
"There's no job more important than protecting our children," he wrote in an article for the newspaper.
"But instead of getting on with the job, and introducing urgent legislation, Ruth Kelly is spending all her energy organising a cover-up.
"Ruth Kelly has shown she's not on top of her job. And if she doesn't know what's going on she shouldn't be in it."