Education bosses say "robust" systems are in place to prevent sex offenders working in the district's schools.

Bradford Council said today there should be no danger of anyone on the sex offenders register coming into contact with children in schools.

Schools in the district are told to check all potential employees through the Criminal Records Bureau. But director of education Phil Green said the system depended on police keeping their records on known sex offenders up to date.

The statement follows Education Secretary Ruth Kelly's admission in the Commons yesterday she did not know exactly how many sex offenders were employed in English schools.

She was speaking after the revelation that a sex offender had been cleared to work as a PE teacher in a school in Norwich because he was not on the Department for Education and Skills' (Dfes) list of banned teachers. Paul Reeve was cleared despite receiving a police caution for accessing internet images of children. The Government has launched an urgent review of similar cases.

Mrs Kelly said yesterday that when people had been cautioned for a sexual offence, but not convicted in court, the law requires a decision by a minister.

She told MPs the Government was launching an "exhaustive review of all such cases in order to confirm the precise number of these individuals, their whereabouts and whether their behaviour has been of concern to the authorities."

When the Telegraph & Argus asked Bradford Council if it could categorically say no sex offenders were working in the district's schools it issued a statement saying: "We issue comprehensive and robust guidelines to schools about the need for Criminal Record Bureau checks on all people, including staff who could have direct contact with children.

"Provided that these checks are carried out in a rigorous and timely fashion, then there should be no danger of any person on the list being employed or otherwise having contact with children."

Dr Tony Rickwood, head teacher at Parkside School, in Cullingworth, said he was confident Bradford's system prevented known sex offenders being employed.

But he was dismayed the Government was only now launching a review, three years after Holly Wells and Jessica Chapman were killed by Ian Huntley who had worked as a school caretaker.

Dr Rickwood said: "The recommendation that came out of the Soham inquiry was an amalgamation of the lists to prevent people falling between two or three different areas which is what seems to have happened in this case."

Tong School head teacher Lyn O'Reilly said Bradford Council and Education Bradford provided very thorough training to schools.

She said: "This is a particular strength in Bradford. I know because my leadership team has just gone through the training. It concentrates not only on Criminal Records Bureau checks but also on looking for gaps in applications or periods people are not prepared to give references for."