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 appeal decision is a blow to Hannah McClure, a student, and Josh Moos, a campaigner for Plane Stupid, who challenged the legality of the "violent" restraint methods used against them when they were contained by officers at the Camp for Climate Action in Bishopsgate in the City of London on April 1 2009. Both now face heavy legal bills.
Mr Moos said it was "a shame" the appeal judges could not see that the police were "out of control".
The day of the demonstrations was the day newspaper seller Ian Tomlinson died after being struck by a police officer at a separate G20 protest at the nearby Royal Exchange.
The police said the extended kettling was necessary to keep violent demonstrators at the Royal Exchange from "hijacking" the more peaceful climate camp, attended by up to 5,000 people.
The High Court ruled last April that there had been no evidence of an imminent breach of the peace to justify the kettle, when a tight police cordon was thrown round the climate camp demonstrators from just after 7pm for more than four hours.
The judges did not rule that kettling was unlawful but criticised "unduly inflexible" arrangements for releasing people. Mr Moos said he became dehydrated after being refused permission to leave.
But the appeal judges disagreed and ruled the police actions were not unlawful.
