Wednesday 16 September 2015 3:14 pm

Uber taxi protest brings London to standstill (again) as black cab drivers demonstrate outside Boris Johnson's Question Time at City Hall

Mayor's Question Time was shut down after police were called to City Hall today, after a security guard was apparently knocked out in scuffle outside the building. 

Black cab drivers were demonstrating outside (and inside) the Southbank venue over ongoing criticism of Transport for London's handling of regulation for private hire car companies, in particular Uber. 

They waved banners calling for Johnson to "stand firm" against "Uber's lobbyists", with suggestions that the ride-sharing taxi app puts public safety at risk. 

But what was a peaceful, albeit rowdy protest, descended into violance after a number of protesters were expelled from the gallery when Johnson dubbed them "luddites".

A security guard was reportedly knocked "unconscious" as tensions rose. The London Ambulance Service has confirmed that one person was taken to hospital for minor injuries. 

The protest is ongoing outside of City Hall however. Police have advised motorists to avoid the area, with the protest causing congestion in nearby roads. 

The iconic London taxis have ground traffic to a halt from Tower Bridge and along Tooley Street towards London Bridge. 

The protest is apparently causing queues from Tower Bridge to East Smithfield and as far south as Borough High Street. 

Pictures posted on social media showed what appeared to be hundreds of protesters turning out in support of black cabs this morning, despite the rain.

Supporters took no small pleasure from the fact the protest had blocked at least one Uber driver.