The Metropolitan Police Commissioner has won an appeal against a High Court ruling over "kettling" tactics during the G20 demonstrations in 2009.
High Court judges declared that officers acted unlawfully in two respects during the protests.
But Lord Neuberger, the Master of the Rolls, sitting in the Court of Appeal with Lord Justice Hughes and Lord Justice Sullivan, ruled that the High Court decision was flawed and allowed the police appeal.
The police practice of "kettling" is the containment of large crowds into small spaces during demonstrations. The police tactic is called kettling in part because the protesters are contained like hot water and steam within a kettle.