Ian Tomlinson's family complained to the IPCC
The Metropolitan Police is to be investigated over its handling of the media following the death of Ian Tomlinson during the G20 protests.
The 47-year-old died minutes after he was pushed over by a policeman.
The Independent Police Complaints Commission inquiry follows complaints that police misinformed the media.
Mr Tomlinson's family say the Met knew its officers had contact with him before his death. The City of London Police force will also be investigated.
Mr Tomlinson, a newspaper seller, had been walking home at the time of the incident on 1 April and was not part of the demonstrations.
His family are concerned the Met released misleading information about the level of contact with Mr Tomlinson until some video footage, which appeared to contradict the Met's account, was published on 7 April.
An initial Scotland Yard statement, issued on the day of Mr Tomlinson's death, said officers had tried to revive him after being alerted to his collapse by a member of the public, and suggested some of the protesters had hampered their efforts.
Six days later, a national newspaper released a video apparently showing Mr Tomlinson being pushed to the ground from behind by a police officer.
IPCC deputy chairman Deborah Glass said: "Not only the Tomlinson family, but also many members of the public and MPs have raised with us concerns about whether the police either misinformed the public about the circumstances of Mr Tomlinson's death or failed to correct misinformation about how he died."
She said the watchdog would look into the family's specific complaint about the content and timing of the Met's media communications on the night of 1 April.
It would also try to determine "the state of knowledge" that the Met and the City of London Police had about any police contact with Ian Tomlinson between 1 April and 7 April, she added.
A Met police spokesman said: "The commissioner has made it clear on a number of occasions that Ian Tomlinson's family deserve, and should expect answers to their questions in relation to his death.
"It is important that there is a transparent process, which provides clarity as to what the MPS [Metropolitan Police Service], City of London Police and the IPCC said and knew regarding the circumstances of Ian Tomlinson's death.
"Therefore we welcome the IPCC investigation and will continue to cooperate fully with them."
This latest inquiry will be separate from the IPCC's ongoing investigation into the circumstances of Mr Tomlinson's death.
The IPCC is also conducting a further three investigations into allegations that officers assaulted members of the public at the G20 protests.