A convicted paedophile has been working with thousands of children from across Sussex.
Nigel Edwards, who was jailed in 1997, was involved in a project teaching children about radio broadcasting.
The news follows a series of revelations about men with sex offences on their record being allowed to work with children.
Inverse Communications, the firm he was working for, has sacked the 53-year-old and said: "At no point has he been unsupervised."
But teachers from the schools involved in the project today told of their shock that another paedophile had slipped through the net.
Matt Trent, a teacher at Polegate School, said: "Anyone working with children in any way is supposed to have full criminal record checks done.
"This has come completely out of the blue and just shows you what can happen if they are not done."
A workshop Edwards was working on in Grimsby has been cancelled and an inquiry launched.
Edwards, from the West Midlands, was given a four-year jail sentence after being found guilty of indecent assault and two counts of a serious sexual offence against a 13-year-old boy.
He also admitted another offence of indecent assault on a male in 1994.
He had been working for the media consultancy group, based in Chichester, which helps schools run short-term radio stations.
Last November, Edwards was at a three-day event in Eastbourne where children from about 20 schools were learning more about radio.
The Argus reported earlier this month that Brighton social worker Gordon Oliver, who committed a string of sex attacks on children, was allowed to carry on working for years after concerns about his behaviour were first raised.
We also revealed that Kevin Hazelwood, a paedophile from Brighton known to Sussex Police, was able to repeatedly rape a nine-year-old girl despite being under community supervision.
Sussex Downs College, which hosted the Eastbourne Youth Radio event, said in a statement: "The college takes matters like this very seriously.
"The college is rigorous with its own Criminal Records Bureau (CRB) checks, which cover all its 1,400 teaching and support staff.
"It is college policy that students are supervised at all times by college lecturers who have been CRB checked.
"With regards to Eastbourne Youth Radio, a team of approved college lecturers and school teachers supervised the students at all times.
"No students were left unsupervised with anyone not employed by the college."
The college is in discussion with the Eastbourne Business Education Partnership, which organised the event, to find out how a convicted sex offender was able to work with children.
More than 2,000 children and teenagers aged between four and 19 from across East Sussex took part in the event, putting together three days of radio programmes, which were broadcast live on a temporary radio station set up by Inverse Communications.
A spokeswoman for the company said: "Inverse Communications is taking these allegations extremely seriously and has launched its own inquiry.
"Mr Edwards worked on a freelance basis for the company and his role was marketing and managing press and publicity.
"At no point on any project has Mr Edwards been unsupervised with young people.
"Inverse Communications will from henceforth CRB check all existing and new staff."
It is believed that Edwards was not on the Sex Offenders' Register as it was set up after his second conviction and is currently not retrospective.
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