More than 80 allegations have been made about G20 police violence
A police officer is being investigated after allegedly writing on a website that he was keen to "bash some long haired hippies" at the G20 protest.
Pc Rob Ward apparently put the note on Facebook on the evening of 1 April, the first day of City of London protests.
A Scotland Yard spokeswoman said: "The matter has been recorded and will be investigated appropriately."
Pc Ward received a written warning but has not been suspended as the inquiry takes place, a police spokesman said.
The Independent Police Complaints Commission (IPCC) received 185 complaints about police behaviour at the protests.
The police officer's profile page on social networking site Facebook contained a message apparently written by Pc Ward at 2017 BST on 1 April.
It stated: "Rob Ward can't wait to bash some long haired hippys up @ the G20."
Twenty minutes later another Facebook user posted a reply that said: "Dats bad but good in da same way lol [laugh out loud]."
The message was later removed from Pc Ward's Facebook page.
The police spokesman said officers from the Directorate of Professional Standards would carry out the initial assessment in the investigation.
Pc Ward could face disciplinary action over the message.
Liberal Democrat home affairs spokesman Chris Huhne said: "There is clearly a worry about the canteen culture of some parts of the Met, which this Facebook posting feeds."
The IPCC received more than 80 complaints from people who said they were assaulted or witnessed an assault by police during the G20 protests.
It also received more than 50 complaints about police tactics.
Ian Tomlinson, a 47-year-old newspaper vendor, died minutes after he was pushed over by a policeman during the demonstrations on 1 April.
The police officer at the centre of that allegation has been suspended and interviewed under caution on suspicion of manslaughter in connection with the death.