Education Secretary Ruth Kelly last night insisted protecting children was her "first priority" after she was criticised for allowing a man on the sex offenders' register to work in a school.

She promised to make "further improvements" to the policies under which she approved Paul Reeve for work as a PE teacher if reforms were found to be necessary.

Mr Reeve was given a job at the Hewett School in Norwich last month despite being cautioned for accessing banned images of children on the internet.

Parents' leaders described the episode as "terrifying" and the Tories accused Ms Kelly of "a serious lapse of judgment" after details of the case emerged.

In her first public comments on the matter, Ms Kelly said in a statement last night: "Our first priority has always been the protection of children.

"Whilst we do not comment on individual cases, decisions have to be taken on the basis of the evidence and within the legal framework.

"We are already reforming the current system by developing a new vetting and bar-ring scheme with the Home Office and police which will provide better protection for children and vulnerable adults.

"I have also asked my officials to review this case to see if improvements are needed.

"If further improvements are needed on the basis of advice received, I won't hesitate in making them."

Earlier yesterday, Midland MP and Schools Minister Jacqui Smith (Redditch) defended Ms Kelly's action and the Department for Education and Skills (DfES) began a review of its policy.

Miss Smith said: "Let's be clear. This person isn't working as a teacher. The system broadly saw that that didn't happen."

She said anybody who wanted to work as a teacher would have a Criminal Records Bureau check.

Asked why the man was approved, she said: "It was a decision taken on the basis of the evidence and within the legal framework.

"But I certainly think that it throws up some very important issues, which is why we are already in the process that we are going through at the moment in designing new legislation to reform and tighten the system, developing a new vetting scheme.

"We'll look at how this case means that we should provide better protection for children.

"We will review this case to see whether it raises any policy issues."

She said the Government would not hesitate to act to close any loopholes.

Mr Reeve was arrested in 2003 by Norfolk Police as part of Operation Ore, the largest inquiry into child pornography undertaken in the UK. He received a police caution for accessing banned images of children on the internet.

He was only stopped from working as a PE teacher when police alerted the school.