London taxi drivers brought Westminster to a standstill in a protest over their ban from Olympic traffic lanes.
More than 200 black cabs arrived in Parliament Square just before 14:00 BST, beeping their horns to tourists' bemusement.
Cab drivers argue they should be able to use the Games Lanes available only to Olympics officials and athletes.
But Transport for London transport commissioner Peter Hendy condemned the action.
He said he had "no sympathy" for the "trumped-up" demonstration.
Jonathan Myers, of the United Cabbies Group union, said: "There will be no access to these lanes for any traffic apart from the Olympics family.
"Taxis are excluded, which is unacceptable and wrong. This is a working city and we need to get around and do our job."
A spokesman for TfL said there had been discussions with black cab drivers since 2009.
He said they would be able to access some of the special lanes to collect fares, including the nearside Games Lane in Park Lane, central London.
John Mason, Director of London Taxi and Private Hire called the protest "completely irresponsible".
He said: "We strongly urge taxi drivers to ignore calls to join these unnecessary protests and instead show why they are regularly voted the best in the world."
The Metropolitan Police said the planned demonstration affected Whitehall and Trafalgar Square as well as Parliament Square.