POLICE are investigating 13 sex offenders who may still be working in schools, Education Secretary Ruth Kelly admitted yesterday as she fought to save her career.

They are among 88 sex offenders not added to the Government's blacklist since Labour came to power in 1997, MPs were told in a statement.

Investigations have established that 42 of the 88 were not working in schools, while police had now assessed most of the rest, Ms Kelly said.

But the Education Secretary was forced to admit information was not yet complete on 13 sex offenders who were still the focus of inquiries.

That was leapt on by Tory education spokesman David Willetts, who said: "There remain key concerns about those child sex offenders who ministers have previously cleared to work in schools.

"This means there are 13 offenders who are free to work with children and who the Department for Education cannot guarantee do not pose a threat to children."

Mr Willetts also pointed out that, of ten registered sex offenders approved to work in schools by Labour ministers, no fewer than five were cleared by Ms Kelly last year.

As expected, Ms Kelly promised to close the loopholes in the system and stop anyone cautioned or convicted of a child sex offence from working in schools.

And, for the first time, people convicted of serious sex offences against adults will also be added automatically to a single, merged blacklist.

Ms Kelly said legislation would be introduced next month, implementing the recommendations of the Bichard report into child safety, which followed the Soham murders.

An independent panel of experts, under ex-Barnado's chief Sir Roger Singleton, would decide who should be barred from working with children - removing the decision from ministers.

Ms Kelly said she deeply regretted the concern provoked by the revelations a teacher had been allowed to work at a Norfolk school, despite being cautioned for paying to download child porn from the Internet.

It later emerged that William Gibson, who was convicted in 1980 for indecent assault of a child, was allowed to teach in County Durham, South Tyneside and Dorset.

The changes were widely welcomed last night.

Councillor Neil Foster, cabinet member for children's services at Durham County Council, said: "This is excellent and reinforces what we have been working on for a number of years with schools. We hope it will ensure the safety of children."

Councillor Alex Cunningham, cabinet member for children and young people at Stockton Council, said: "It is absolutely critical that everything possible is done to protect our children.

"I believe the new measures announced will be a significant step forward."