Most police officers receive two days of public order training every year
A watchdog has said the Metropolitan Police's planning for the London G20 protests in April was inadequate.
Her Majesty's Inspectorate of Constabulary said the force had responded well to some of the challenges posed by the world summit.
But it said the force had not planned for the peaceful but highly disruptive Climate Camp in the City of London.
One man died after the London protests and investigators are looking at other formal complaints about police actions.
In his wide-ranging report, the inspector of constabulary Denis O'Connor said police tactics had been far too focused on tackling violence, such as the sporadic clashes outside the Bank of England, rather than facilitating peaceful protests during other parts of the day.
Inspector of constabulary Denis O'Connor: "Police tactics need to change"
He supported the police's controversial "kettling" tactics to surround crowds - but said they had been inconsistently applied during the G20.
On some occasions officers had allowed people to pass through security cordons - but at other times protesters and the public had been completely contained.
This inconsistent application of a key tactic had been very carefully documented by the public who had uploaded footage to the internet from their camera phones.
This had exposed the police to unprecedented scrutiny, the report said, raising important questions about the police's broader approach to policing demonstrations.
Mr O'Connor said the current protest training manual was insufficient and needed to be rethought before the 2012 Olympics. The starting point for policing protests should neither be whether they were lawful nor unlawful, but a presumption of facilitating peaceful activity, he said.
"What the review identifies is that the world is changing and the police need to think about changing their approach to policing protests," he said.
"We live in an age where public consent of policing cannot be assumed and policing, including public order policing, should be designed to win the consent of the public."
Mr O'Connor said that the police should allow demonstrators clear routes out of a kettle cordon and guarantee access to toilets or other facilities.
Members of the public who were inadvertently caught up, or those vulnerable or distressed, should always be allowed to leave.
Police separate groups of protesters in the City
One of the crucial outstanding issues is the investigation into the death of newspaper seller Ian Tomlinson.
He was trying to return home when he was caught up in one demonstration and struck and pushed by a police officer.
Two post-mortem examinations have come to different conclusions as to the cause of death.
The result of a third post-mortem examination conducted for the Met remains confidential.
The investigation into the death by the Independent Police Complaints Commission is unlikely to be completed before 2010.
The HMIC also commissioned a survey into public attitudes towards protests - and found respondents divided over the tactics used during the G20.
'How well did the police do during the G20 protests?'
Not well: 45%
Don't know: 9%
Source: Ipsos-Mori poll of 1,339 adults for HMIC
Metropolitan Police Assistant Commissioner Chris Allison said the HMIC review, commissioned by the force, had recognised the exceptional challenge posed by the G20 summit and the pressures placed on the frontline officers.
"We have clear duties under the law to facilitate protest, minimise the impact it has on others and maintain peace on our streets," he said.
"As the report recognises, balancing these competing responsibilities is not easy, but we want to address areas of public concern and move forward.
"Whilst containment is the most effective tactic that we currently have to deal with violence and disorder in these types of situation, [we have] always acknowledged that there are challenges associated with it."
The report comes a week after MPs on the Home Affairs Select Committee concluded there had been too many inexperienced officers on the frontline of the G20 protests.
And Sir Hugh Orde, the incoming president of the Association of Chief Police Officers, is using his first speech on Wednesday to call on constabularies to learn from his experiences in Northern Ireland.
He is urging chief constables to place human rights and consent at the core of policing and to recognise the importance of intense informal public scrutiny created by internet technology.
The graphic above shows how the police contain crowds of protesters, using London's Bank of England as an example. Protesters begin to gather from roads to the north and east, and are guided towards a central location by police.
A crowd of protesters forms outside the bank, as more join the demonstration from the surrounding roads. Police wearing high-visibility jackets begin to form a cordon around the crowd.
The police cordon has now entirely contained the crowd, but protesters can still enter if they so wish. Equally, people may leave the "kettle" through an exit point to the south or west, away from the main protest.
As the crowd grows and police perceive a threat, the cordon becomes a permanent "kettle" strengthened by riot police waiting in nearby vans. Nobody can enter or leave - possibly for hours.
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