David Blaxhall's candid camera managed to video up a 14-year-old's skirt in a classroom in what was described as a "disgraceful" abuse of trust.

But when the camcorder was spotted, pupils turned the tables on him by recording his actions on a mobile phone.

Blaxhall (49), of Longridge Heath, Brierfield, described it as a "morality bypass" after his wife left him for another man, Preston Crown Court heard.

He admitted four charges of taking indecent photos and three of making indecent photos. He was given a community order, involving three years' supervision and a requirement to go on community sex offender programme.

The first four offences dated to 2006, at a school in Blackburn, when Blaxhall ran a project for several schools, training pupils on radio broacasting.

Mr Hugh McKee (prosecuting) said around 20 pupils, including girls, were involved in the project and one became concerned Blaxhall was using a camcorder beneath the desk where he was sitting, to film her lower body.

"The pupils decided not to do anything until they had proof," he said. "The next day she could see the defendant was again using a camcorder beneath the desk to film her lower body. On this occasion another friend used a mobile phone to record what the defendant was doing."

Police found a 41-minute video tape on the front seat of his car, with several stills taken from it. His home was searched and at least two computers taken and several indecent images found on them - four at level one, two at level two and one at level three of seriousness. The photos taken at school were level one, the least serious category.

Blaxhall, who had worked for radio stations in East Lancashire,was of previous good character.

Mr Gerard Doran (defending) said the court would be troubled a man of Blaxhall's age and position should depart from a positive and productive life. "He described it, in his own words, as a period of time 'when my morality and good character had a bypass'," he said.

Mr Doran went on: "He recognises he has acted within a moment of madness. It wasn't for a very long time that he was called to the lower court. He suffered significantly with feelings of paranoia every time the door would knock or the postman would arrive. He feared that was the day when the letter would come for him to be brought to court."

He said that since his arrest, he had sought to challenge his behaviour and had seen a counsellor.

The judge directed that Blaxhall should be on the sex offenders list for five years and subject to a 10-year sexual offences prevention order, banning him from unsupervised association or contact with under 16s. It also bars him from entering schools or perimeter grounds and any employment that would bing him into contact with children.

Judge Anthony Russell told him: "What is serious about this case is the disgraceful abuse of trust.

"It has resulted in considerable distress, not merely to the family of the girl and girl herself, but other pupils and no doubt their families who may wonder whether on other occasions you have done it to other children.

"That was an action of which you should be thoroughly ashamed."