In pictures: Cab drivers go slow over mobile app Uber

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  Up to an estimated 12,000 black-cab and licensed taxi drivers took part in the 'go-slow' demonstration in central London, to protest against Uber, a taxi-booking mobile app. Luke MacGregor / Reuters

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  Drivers' unions in London are concerned that the rise of Uber could cause people to travel with unlicensed cabs and taxis. Luke MacGregor / Reuters

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  Up to an estimated 12,000 black-cab and licensed taxi drivers took part in the 'go-slow' demonstration in central London, to protest against Uber, a taxi-booking mobile app. Luke MacGregor / Reuters

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  London's drivers unions say Uber, launched in 2009 and currently in operation in more than 70 cities across 37 countries, there is a lack of regulation behind the mobile app. Dan Kitwood / Getty Images

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  Police officers look on during a protest by London black-cab drivers against Uber, a mobile phone app. Carl Court / AFP

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  A demonstrator holds a placard during a protest by London black cab drivers against Uber, a mobile phone app. Carl Court / AFP

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  In Berlin, supporters of online ride-sharing apps hold up signs demanding an end to the taxi monopoly at a demonstration by taxi drivers at Olympia Stadium on June 11. Sean Gallup / Getty Images

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  Taxi drivers gather next to the Olympia Stadium in Berlin, Germany to protest ride-sharing apps Wundercar and Uber. Sean Gallup / Getty Images

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  Hundreds of taxi drivers in Berlin gathered to protest against new apps like Wundercar and Uber which they claim are undermining their livelihood and creating unfair competition. Sean Gallup / Getty Images

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  While Uber is not currently operating in Madrid, taxi drivers are protesting against its imminent launch and the government's lack of regulation on the app. Uber services are only available in Barcelona at the moment. Hugo Ortuno / EPA

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  While Uber is not currently operating in Madrid, taxi drivers are protesting against its imminent launch and the government's lack of regulation on the app. Uber services are only available in Barcelona at the moment. Hugo Ortuno / EPA

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  In Rio de Janeiro, taxi drivers staged a rally and partial road blockage a day before the city plays host of the Fifa World Cup. Joe Raedle / Getty Images

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  Above, a yellow ribbon indicates a striking Paris taxi. Taxi drivers in teamed up in large numbers to slow traffic to a snail’s pace on major motorway access routes into the capital. Philippe Wojazer / Reuters

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  Above, a yellow ribbon indicates a striking Paris taxi. Taxi drivers in teamed up in large numbers to slow traffic to a snail’s pace on major motorway access routes into the capital. Philippe Wojazer / Reuters

Motorists faced huge delays in central London and other cities on Wednesday after black-cab drivers blocked traffic in a protest over the taxi-booking mobile app Uber.