A conviction for criminal activity - including crimes of sexual assault - is not a bar to the acquisition of a licence to drive a taxi, it has emerged. But a Garda spokesman said the awarding of a licence to the X-case man was "an error".
Fine Gael has called for new laws regulating the taxi service.
According to the Garda Traffic Division, which controls the granting of Public Service Vehicle (PSV) licences through the Carriage Office, the courts have made it "explicitly clear" that the holding of a criminal conviction should not be a bar on the acquisition of a PSV licence.
While it maintains the strictures on getting a PSV licence are rigidly enforced, the division has confirmed it is aware of other divisions investigating at least one other serious sexual assault, which allegedly happened in the Phoenix Park, Dublin, since last Christmas.
Sources in the taxi drivers' unions suggest the number of sexual assaults under investigation may be higher.
Currently, to qualify as a taxi driver a person must have a suitable car which has an NCT certificate. He or she must also pay €6,350 to Dublin Corporation and just €5 for a PSV licence. As part of the PSV licence application the person must sit a geographical "knowledge test" of the taxi meter area, and satisfy the Garda of their suitability of character.
If the gardaí refuse, the applicant has the right to appeal to the district courts.
However, the Fine Gael spokeswoman on traffic, Ms Olivia Mitchell, claimed yesterday that 20 per cent of taxi applicants last year had criminal convictions, while the courts had found in favour of the applicants in the last three cases to come before them.
According to Ms Mitchell this was evidence a new PSV Act was urgently needed.
"One of the three most recently appealed licence decisions went in favour of someone with a previous conviction for a sexual offence.
"This is an intolerable situation and requires new legislation to prohibit the granting of taxi PSV licences - at least to sexual offenders."
Ms Mitchell pointed out that following deregulation the Minister responsible, the Minister for State at the Department of the Environment, Mr Robert Molloy TD, had increased the time for renewal of licences from one year to five years.
"This means a driver could be serving a prison sentence and still be in possession of a licence to drive vulnerable young people immediately on release," she said.
The Minister was not available for comment yesterday.