A heavily bleeding young woman was blocked from leaving G20 protests after being pushed back violently by police officers with shields.
The woman, 23, was caught up in clashes between demonstrators and officers at the impromptu Climate Camp in Bishopsgate, in the City of London, on April 1.
She was later told by a doctor there was a "low" chance she may have suffered a miscarriage, but the woman did not think she was pregnant.
An inquiry by the Independent Police Complaints Commission (IPCC) found the woman was stopped from leaving the protest for up to five hours.
She claimed to have suffered bruising on her arms and legs when she was kicked and pushed by officers holding shields and batons. When the intimate bleeding started some time later she was blocked from leaving the area by lines of police officers.
Officials agreed the woman was forcibly pushed back by an officer using a "short shield" and said her experience was typical of many peaceful protesters.
They said the tactic was developed by the Metropolitan Police and had not been approved nationally by senior officers.
The IPCC called on the police to make immediate changes to the way they control public protests. They said police must review public order training, warn participants of their plans and allow vulnerable people to leave demonstrations.
The recommendations mirror those made by Her Majesty's Inspectorate of Constabulary (HMIC) last month.
A Metropolitan Police spokesman said: "It is only right and proper that public complaints are investigated thoroughly, and where appropriate, independently. Though we note that the medical opinion was that there was a low probabilgity of the complainant being pregnant, there is a real opportunity for lessons to be learnt here."
