Motorists have faced long delays around Aldwych, central London, after scores of black cab drivers blocked streets in a protest over illegal minicabs.
Licensed black cab drivers claim the minicab trade is not policed properly and unlicensed drivers touting for business pose a danger to the public.
The blockade began at 1500 BST leading to delays near the Strand and roads leading to and from Waterloo Bridge.
Drivers drove around the Aldwych roundabout leading to long queues.
The hour-long protest had a knock-on effect on traffic in the run-up to rush hour.
More than 6,000 illegal drivers have been arrested since 2003, Metropolitan Police said.
Black cab drivers have accused the police, the mayor and local authorities of not doing enough to tackle illegal minicabs.
They have claimed their complaints are ignored and passengers lives are being put at risk.
A spokesman for the protesting drivers said: "It is time that the various bodies start to treat the licensed London taxi trade with the respect it deserves.
"It is consistently voted the best taxi trade in the world and does more for London's tourist trade than all the above authorities put together.
"We are sorry that we have to block the streets to make our voices heard, but we feel we have no other option."
A Metropolitan Police spokesman advised motorists to avoid travelling through the area during the protest.
A spokesman for its Cabs Enforcement Unit (CEU) said: "Since 2003, the Safer Transport Command has arrested more than 6,000 illegal cab drivers and has doubled the number of dedicated cab enforcement officers in the capital to 68.
"The CEU carry out operations on a daily basis in line with current intelligence on touting behaviour.
"They also co-operate with clubs to crack down on the touts who operate in the area and ensure compliance with regulations and importantly enhance the safety of the travelling public."
A spokesman for the Mayor of London said: "We introduced the one strike and out policy for both drivers and operators and have revoked over 250 licences to date.
"Any operator found to be employing staff that we find touting on street will have their licence revoked."