Fewer than half of passengers know whether their minicab is licensed, according to research by the London Assembly.
It found while 85 per cent of users say its important to feel safe in a taxi, far fewer actually knew how to identify a legal vehicle.
However two thirds of black cab passengers knew how to identify whether their taxi was licensed.
Transport for London said it is working with the owners of The Shard to introduce a taxi rank outside the building as they expressed their disappointment that cab drivers went ahead with a protest.
Hundreds of cab drivers filled the streets near Europe's tallest building in protest at TfL.
Garrett Emmerson, TfL’s Chief Operating Officer for Surface Transport, said:
London's taxi drivers converged on London Bridge today to protest against TfL's decision not to place a taxi rank outside the Shard.
The opening of a new hotel at the Shard today is to be marked by a protest by taxi drivers.
The cab section of the Unite union claim Transport for London is refusing to put a taxi rank near to the building's entrance on St Thomas Street.
The union claims Boris Johnson is not giving taxi services enough consideration as part of the capital's transport network.
Black cab fares in the capital are going up and could rise again as early as next January.From April 5, London taxi fares will increase by an average of 0.7%, Transport for London (TfL) announced today.
TfL said the below-inflation increase was the lowest since it took responsibility for licensing taxis in 2000 and the rise equated to just 9p more on an average fare.
Taxi drivers will converge on Trafalgar Square this morning in protest over planned tax hikes on biodiesel produced with used cooking oil.
The cab drivers claim the tax increase will force many of them to go back to fossil fuels - which will lead to an increase carbon emissions.