BBC Online :
Transport in major European cities has been disrupted by twin strikes, affecting taxis and rail services.
Two-thirds of trains were not running in some areas of France in a strike against reforms and taxis were blocking traffic around some airports.
Cab-drivers are protesting at what they regard as a lack of regulation of rival mobile service Uber.
The biggest taxi associations in the Spanish capital asked their drivers to observe a 24-hour stoppage until 06:00 on Thursday morning. More than 15,000 licensed vehicles operate in Madrid, Spanish media say.
The London protest was to start in Trafalgar Square at 14:00 BST (13:00 GMT), with taxi drivers arguing that the Uber mobile app, which originated in the US, was tantamount to a taxi meter, which only black cabs are legally entitled to use in London.
Up to 12,000 drivers are expected to take part in the protest.
The Metropolitan Police said conditions had been imposed on protesters after they failed to meet with officers to discuss their plans.
In Milan, in northern Italy, a protest was taking place throughout Wednesday, although disruption was not expected to be on a similar scale as elsewhere, with boycotts expected of key sites such as railway stations and squares.
