Ms Nicola Fisher was seen on YouTube footage shouting at a line of police when Sergeant Delroy Smellie appeared to slap her face with his gloved hand and hit the back of her legs with a baton.
The incident happened during a vigil for Ian Tomlinson who had died the previous day of a heart attack shortly after being forcefully pushed by a different police officer.
The police management of the protesters in the City of London over the several days of the G20 summit has been called heavy-handed. It included use of "kettling" where crowds were moved into a small area and kept there for a long time by tight lines of police.
A Crown Prosecution Service spokesman said, "The Crown Prosecution Service reviewed a file of evidence provided by the Independent Police Complaints Commission following their investigation into Ms Fisher's allegation.
"A summons has been served on PS Smellie who will appear at City of Westminster Magistrates Court on 16th November 2009."
Within two weeks of the event, 145 complaints had been made to the Independent Police Complaints Commission (IPCC) about excessive force by individual police or the general crowd management.
Internet Coverage
Forty of these contacts were dismissed from further investigation because they do not qualify under the Police Reform Act.
Video footage of incidents of police action around the G20 event was posted on websites and social networks almost instantaneously. The majority of the dismissed claims were from people who were not directly involved in incidents, but later viewed them online or on television.
Without internet coverage, Ms Fisher thinks she would not have been believed.
Since the incident Ms Fisher has come under tabloid scrutiny and been accused of being a "shoplifter", sharing a flat with an overweight man and asking Max Clifford to be her agent.
On the day of the incident Ms Fisher says she went away from the scene to investigate her leg which felt wet. While investigating, another policeman told her she must cover her legs or she would be charged with indecent exposure.
She also states that PS Smellie had his badge number covered up.
The Metropolitan Police say they take allegations against their staff very seriously but will not comment on the specific cases.
In a statement they said: "Every officer is accountable under law and fully aware of the scrutiny that their actions can be held open to. The decision to use force is made by the individual police officer, and they must account for that."
The investigation of Ian Tomlinson’s death is separate and may involve manslaughter charges so it is likely to be a lengthy process. However, there are strong urges for reform by Her Majesty's Inspectorate of Constabulary, whose report stated that the police's tactics were inadequate, and by The IPCC which wants immediate changes to the policing of protests.
