Roberts, 68, from Sheerness, Kent, denies any wrongdoing, but the 52-page report says: 'The complaints against Mr Roberts are serious. He manipulated his position, influence and experience for the purposes of his own sexual gratification. He did so by taking advantage of the vulnerability of his students.'
Mark Costiff, of Crawley, Sussex, said Roberts assaulted him after persuading him to visit his home for coaching.
Mr Costiff, now 40, was 16 at the time. He agreed to be identified by The Mail on Sunday and said: 'I didn't report it at the time because he suppressed me and I was embarrassed. He made me feel that if anything wrong had happened, it was my fault.
'It was horrendous. But he was very clever at covering it up. I was assured by the BJA that he would never be allowed to coach children again. I'm shocked by the decision not to bar him - it's scary to think he could get involved with young people again.'
Roberts was suspended as a senior coach in 2009 after five judo players made complaints. Kent Police carried out two investigations but the Crown Prosecution Service decided there was insufficient evidence to bring charges.
The tribunal report reveals that Roberts was once charged with indecent assault. He was found not guilty at Medway Magistrates Court in Kent in 1999. He told the MoS this week: 'I categorically deny all of the allegations.' He added that all his legal costs had been paid following his acquittal by Medway magistrates.
A senior source within the sport said: 'As far as the BJA is concerned, Roberts remains a danger to children. He will never be allowed to coach judo in this country again.'
DBS operations director Janet Gauld declined to comment. Miss Howey said: 'I was totally unaware of the allegations against Alan Roberts. I was shocked when they emerged.'
- Mail On Sunday