Hundreds of black cabs halted traffic in parts of central London in protest against a scheme that helps people get minicabs in the city's West End.
Taxi drivers said Westminster Council's scheme was promoting what they called "illegal" minicab ranks in Leicester Square, denying fares to black cabs.
The London Taxi Drivers Association (LTDA) and the London Cab Drivers Club (LCDC) organised the protest.
The council said the aim was to meet a shortage of cabs in the West End.
Hundreds of black cabs clogged the roads around Trafalgar Square and down Whitehall to Downing Street in what organisers said was a "drive-in" protest.
The trial marshall scheme - which has proved popular with customers - was set up by Heart of London Business Alliance with West1 MiniCabs, Westminster City Council and the Metropolitan Police.
The minicabs gather at a bus bay in Whitcomb Street, Leicester Square, from Thursdays through to Saturdays between 2100 GMT and 0400 GMT.
Marshalls guide people to a booking booth where they pay for their ride and are then guided to the minicab.
Black cab drivers said they would seek a judicial review of the scheme.
A statement from organisers said: "Minicabs are only allowed to accept pre-booked hirings over the telephone via a licensed office."
They said the demonstration would be first of many by black cabs.
Martin Low, director of transportation at Westminster Council, said: "This is about getting people home safely at night and there is no room for protectionist trade measures where this kind of safety is concerned.
"The scheme, which is still in a trial period, aims to squeeze out illegal touts by publicising and directing people to the information centre (ticket booth) in Leicester Square.
"It was never intended to replace black cabs.
"We would welcome ideas from black cab drivers on how to increase their availability in the West End, particularly in the early hours of the morning when the clubs close."