WHEN biology supply teacher Amy Gehring famously admitted last week she had staged illicit advanced sex education lessons with a pupil she set school alarm bells ringing.

The teacher was cleared by a court of indecent assault on two comprehensive pupils -- but said afterwards she had sex with a 16-year-old boy in another school in the south of England.

At the same time a Blackburn high school head revealed how seven different people had taught maths to one of his classes because of staff shortages.

So what safeguards are in place in East Lancashire to make sure stranger teachers are not a danger, too?

Supply agencies have mushroomed in the wake of the nationwide teacher recruitment crisis and it's now a £400million-a-year business.

But a spokesman for Lancashire County Council said that even if casual teachers came via an agency, County Hall checked them as thoroughly as permanent staff. He added: "Amy Gehring was employed by a Surrey school through a commercial agency. Schools in Lancashire have the freedom to use commercial agencies if they wish, but we also operate our own supply teacher register to assist schools with sudden staff shortages.

"And all our supply staff are required to have the same level of police clearance as our permanent teachers, and every teacher on our supply register will have had their professional background checked. We insist that their references include their most recent employer."

From March 1 local education authorities will be also able to seek information about potential supply teachers from the newly-created Criminal Records Bureau.

"This will give us access to enhanced information held locally by every police force in the country, as well as national records held under the Protection of Children Act List," the spokesman said. He added: "Concerns about the behaviour of any employee - even those of a commercial agency - in relation to the safety and protection of children have to be taken seriously and, if necessary, would be referred through to the social services directorate's child protection team and the police for investigation."

Blackburn with Darwen Council's director of education and lifelong learning Peter Morgan added: "When the Criminal Records Bureau comes into force in March it will have responsibility for checking teaching staff and we will have to register with them."