One was on bail charged with attempted rape and one in 10 had no minicab licence, police found in a check of 1,000 drivers earlier this year.
The findings were disclosed yesterday in a television programme which has prompted councillors in Glasgow to seek greater powers to regulate minicab businesses.
The city was said to be without effective policing of the minicab sector in the absence of its four-man enforcing team, who said they were encouraged to take indefinite sick leave after harassment and hostility from minicab operators.
The unit was set up in 1982 with powers to stop and check cars, but one of the team, Tommy McCaig, said he and colleagues had a barrage of telephone threats.
At one point, cabs were sent to the homes of all four - telling them they were to be taken to Glasgow airport - "and you're not coming back".
The BBC Scotland programme Frontline Scotland also highlights the case of a seven-year-old girl killed by a minicab driver who allegedly had three speeding convictions, one three weeks before her death.
The police check, Operation Stance, was prompted by fears about the quality of cars and drivers involved in minicab work, and by fears that it could be a front for other illegal activity.
Unlike traditional black taxis, Glasgow minicab drivers have to be licensed - but not their operators or companies.
Harry Gangol, chairman of the Glasgow Private Hire Association, said the trade had been asking the council for 12 years to licence the companies, but without success.
John Moines, chairman of Glasgow's licensing committee, said he was unaware that operators did not have to be licensed, but would now seek to have the loophole plugged.
"I am very concerned and no doubt from this interview the city of Glasgow will now be working hard to get to confidence of the general public back on the private hires."
Glasgow city council said an "urgent review" of security surrounding minicabs was ordered on 20 March. It denied the four enforcement officers had left because of threats, saying they were unhappy about new terms and conditions and two took early retirement and two voluntary redundancy.Reuse content