Police today issued a photograph of a man wanted in connection with a violent assault on a security guard in a protest by black cab drivers at London's City Hall.
The guard was knocked unconscious when trouble flared on Wednesday.
Scotland Yard said that at around 9 am a large group of demonstrators gathered outside as part of a spontaneous protest. Around 80 of them were allowed into the public gallery during Mayor's Question Time and others were granted access to the ninth floor.
At about 10.50 a group of around 20 protesters forced their way inside, a Yard spokesman said. As they did so, a security guard was pushed over and knocked unconscious.
Once inside, the group attempted to enter the public gallery but were prevented by security staff and police officers, some of whom were assaulted.
The injured guard was taken to hospital where he was treated for concussion and released later that day.
The Metropolitan Police's Public Order Investigation Team is investigating. Detective Chief Inspector Andy Barnes said: "This went far beyond peaceful protest and is completely unacceptable. Our team are now working through CCTV and will be looking to identify a number of people wanted in relation to this violent incident. Today we have released one image of a suspect in relation to the most violent assault on the security guard. I expect more to follow soon."
The suspect is described as white, around 50, about 6 ft tall with a partly shaved head and a receding hairline. He was wearing black leather trousers and a black leather motorcycle jacket with a light brown stripe on the arms.
Boris Johnson was forced to abandon the meeting after taxi drivers began shouting from the public gallery when he branded them "luddites".
The cabbies gathered amid ongoing criticism of Transport for London's handling of regulation for private hire car companies, including the taxi app Uber.
Mr Johnson said he was "shocked" following the incident, while Scotland Yard has said it received two allegations of assault but no arrests have been made.
Writing on Twitter, Mr Johnson said: "Vital Londoners see democratic process in action but behaviour of some cabbies at MQTs today undermines that. Also shocked that 3 City Hall security staff hurt following suspension of Mayor's Question Time - no excuse for violence."
Anyone with information was asked to contact the Met's Public Order Crime Unit on 020 8246 0068, or, if wishing to remain anonymous, Crimestoppers on 0800 555 111.