Secret intelligence files seen by this newspaper show some private hire businesses in Glasgow, Edinburgh, Dundee and beyond have been infiltrated by major underworld figures.
Detectives reported that 20% of the private hire firms in the Strathclyde force area – the country's biggest – were "linked with general criminal activity". Officers warned that ten "operated as part of organised crime groups".
The files reveal the spread of Glasgow-based criminal groups into taxi business across the country.
Justice Secretary Kenny MacAskill, who has declared war on gangster taxis with a tough new legislative clampdown, has already warned of attempts to infiltrate the Edinburgh market.
The intelligence confirms detectives believe a single business with crime links has been attempting to expand its operations in the capital.
The secret files also reveal there are two crime-linked firms in the Central Scotland police area and one each in Dumfries and Galloway and Tayside.
A police source said: "We should all be very worried about this. Do you really want to get into a car from one of these firms?"
Graeme Pearson, a former head of the Scottish Crime and Drug Enforcement Agency, said crime-controlled private hire firms were now "almost omnipresent" in parts of Scotland.
Pearson, now a professor at Glasgow University's Institute for the Study of Serious Organised Crime, said the police intelligence confirmed what many people in many communities already knew: that criminals are running at least some of their private hire taxis.
He said: "Almost every taxi in some communities is linked with organised crime."
According to the intelligence files, organised crime groups started moving into the private hire business in the west of Scotland in the early 1990s, mostly to launder money.
Pearson said gangland figures were using the cars "for their own messages". Gangsters were summoning their own cars to deliver drugs and prostitutes, mobilise their enforcers and, increasingly, to keep and eye on communities where they vie with the police and government for authority.
Senior police sources hope rules proposed by the Scottish Government to force private hire firms to license their radio rooms will make it harder for crime groups to move into the taxi markets in Fife, the north and the north-east.
A Scottish Government spokesman said: "Tackling serious organised crime is one of the Scottish Government's top priorities. Where it infiltrates legitimate business, like the private hire trade, we are determined to take action."