Freedom of Information requests to councils and police authorities across the West Midlands region discovered that over the past three years 209 people with previous convictions have been given a licence, despite criminal records checks being carried out.
In Wolverhampton, a man who between 1985 and 2005 had carried out more than 30 offences was, in 2006, deemed suitable to become a taxi driver.
A spokesman for Wolverhampton City Council said the licensing of private hire and hackney carriages was taken seriously.
"The council has received no complaints regarding this driver since the private licence was granted in 2006," the spokesman said.
There are no official rules about licensing taxi drivers. Instead, councils tend to follow various guidelines, one of which is issued by the Department of Transport.
In Worcester, there are several drivers with criminal convictions.
A spokesman for the council's licensing committee said they followed guidelines issued by the Metropolitan Police and by the Lord Chief Justice.
"The third criteria is whether we would allow our daughter, if [we] had one, to get in the cab," a spokesman said.
He said convictions for drugs and sexual offences were "a complete no no" but added that was not stipulated in the council's guidelines.
A spokesman for the National Taxi Association said people with previous convictions tended to have their applications decided on merit.
Threats to kill
"If someone does have a lot of previous convictions he is likely to have to go before a council and explain himself," he said.
More checks to police authorities revealed that 250 crimes had been carried out by licensed taxi drivers over the past three years, including rape and making threats to kill.
The National Taxi Association spokesman said magistrates and police would inform a council of a conviction.
"If it is a serious offence they have the power to suspend a driver," he said.
In November 2009, Stoke-on-Trent taxi driver Mohammed Qaddier was found guilty of causing death by dangerous driving.
Katie Bennett, 21, suffered massive head injuries when she tumbled from the cab in Newchapel in May 2008.
The Inside Out investigation revealed that Qaddier had previously had his licence taken away from him by the city council for plying his trade illegally.
In 2004, it was given back to him by the city's magistrates.
Her father Philip Bennett said the fact that people with convictions were getting jobs as drivers was scandalous.
"Whoever is putting them in a position of taxi driving, with those sort of convictions, wants their heads feeling.
"They are no better than the people they are giving licences to," he said.
Last year, councils across the West Midlands region took £4.5m in taxi licensing fees.
The GMB, the taxi driver's union, said the system needed to be tightened.
"What we don't want is a tick box system saying a check is done and the licence issued," a spokesman said.
"The policy must be robust. It must take into account the nature of the offence and does it have any effect on the job they are doing."
Wolverhampton City Council, and others, have now said they will review their guidelines.
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