EDUCATION Secretary Ruth Kelly is at the centre of a row on Monday after it emerged she cleared a registered sex offender to work in schools.

The man was only prevented from starting work as a PE teacher when police alerted the head teacher.

Ms Kelly, the MP for Bolton West, considered evidence that he had accessed paedophile websites inconclusive and so did not place him on the list of those barred from working in schools.

Police officers, who had warned he was a risk, are said to have deep reservations about her decision to overrule their risk assessment.

Ms Kelly is understood to believe that her decision was correct, but has ordered a policy review amid concern from child protection experts.

The case puts more pressure on her at a time when there is dissent among Labour MPs over the Government's education reforms.

The Shadow Education Secretary, David Willetts, called her decision over the PE teacher "extraordinary".

"It is a serious lapse of judgment and raises wider questions about the role of the Secretary of State in individual cases like this," said Mr Willetts.

The Education Department's list of people banned from working in schools is known as "list 99".

Mr Willetts said: "The Government needs urgently to look at how someone can be on the sex offenders' register and yet not be on its own list 99, barring people from working with children.

"This needs to be tackled to restore people's confidence in the integrity of teaching appointments."

The PE teacher had been placed on the sex offenders' register without being convicted of an offence.

Ms Kelly decided not to blacklist him and he was given a job at the Hewett School in Norwich last month.

The Department for Education wrote to Norfolk County Council saying that Ms Kelly had "considered all aspects of the case, including sex offender registration, and decided that the risks of the teacher being allowed to continue teaching were acceptable".

However, the teacher was suspended before he could take up the job following protests from police.

Simon Morgan, spokesman for the Norfolk force, said: "Swift action was taken as soon as this matter came to our attention."

Natalie Cronin, of the NSPCC, said the children's charity had been "concerned for some time" that the decision to blacklist someone rests with the Education Secretary and not experts.

"It is not clear whether civil servants have the degree of knowledge necessary to make such a decision," she said.

Lisa Christensen, of Norfolk Social Services, said: "This case highlights a serious policy contradiction that we are keen that the Education Department addresses as a matter of urgency."

The school's head, Tom Samain, and governors' chairman, Marion Wright, voiced concern in a statement.

"The person concerned is no longer employed and there will be a full examination of the process in this case," they said.

"This is the first time we have had such a case and received such a notification from the Department of Education.

"We are concerned at the policy contradictions it throws up, and have raised our concerns with the Department."

The Department of Education later announced it was reviewing policy in the light of the case.

"We are already reforming and tightening the system by developing a new vetting and barring scheme with the Home Office and police," a spokesman said.

"If further action is needed to improve the system, we will not hesitate in taking it."

The 2002 case of Holly Wells and Jessica Chapman, who were murdered by school caretaker Ian Huntley, highlighted concerns about those working with children.

Huntley had slipped through police checks that were supposed to stop those who might pose a danger to youngsters.

The case prompted the Bichard Inquiry, which called for more stringent vetting of those working with children.