Tom Samain, head of the Hewett school in Norwich, said he has risked his school’s reputation to ensure that necessary changes are made to the system.

Paul Reeve was employed to teach PE at Hewett in December, despite having been cautioned for accessing banned images of children on the internet.

Mr Reeve had been arrested in 2003, as part of the Operation Ore inquiry into child pornography. He worked at Hewett for five days, before police tipped off the school.

Ruth Kelly, Education Secretary, had ruled that Mr Reeve should not be placed on list 99, which bars those on it from working with children. Ms Kelly has since admitted that there are more sex offenders not on this list. She has announced an inquiry into these cases.

The incident has put her under fire from the national media. Kevin Maguire, in the Daily Mirror, awarded Ms Kelly a dunce’s cap, and said that she had been “threatened with exclusion from Government High by principal Tony Blair”. But Jacqui Smith, schools minister, defended Ms Kelly’s actions on Radio 4‘s Today programme.

Mr Samain has no plans to take legal action. “There’s been one hell of a fuss,” he said. “I knew the school would come in for a large share of criticism. But I’d rather see that fuss now, than a huge national tragedy in two years’ time. The debate needs to be started.”

After the murders of two Soham schoolgirls in 2002, an inquiry by Michael Bichard called for more stringent vetting of anyone working with children.

But Mr Samain believes that these procedures need to be reviewed urgently.

“This needs to be No. 1, in terms of importance and urgency,” he said. “I want to see changes occurring.” Lisa Christensen, Norwich director of children’s services, said: “This case highlights a serious policy contradiction, that we are keen the Department for Education and Skills addresses as a matter of urgency.”