Officers used the controversial tactic of "kettling" - holding people in one place for long periods - during the demo in the City of London in April.

But a committee of MPs has said the practice cannot always be justified, that it is not acceptable to impose a blanket ban on movement and that peaceful protesters should be allowed to leave.

More than 35,000 people took to the streets of the capital as world leaders met over two days at the beginning of April.

Scotland Yard has been strongly criticised over the death of newspaper seller Ian Tomlinson who was pushed to the ground during clashes.

Members said they were concerned untrained and inexperienced officers were left in such a "highly combustible atmosphere" at the frontline of the protests.

"The police's doctrine must remain focused on allowing this protest to happen peacefully."