Police today admitted that they conducted illegal "stop and searches" on 11-year-old twins and other activists at an environmental demonstration.
The chief constable of Kent, Mike Fuller, made the admission in a high court case that challenged the tactics he used to contain a demonstration against a proposed coal-fired power station.
He and his force have already been heavily criticised over their handling of the demonstration, after allegations of brutality by officers who hid their badge numbers, and the use of loud music to stop activists sleeping.
The admission came after a ruling by the European court of human rights in a separate case that it was unlawful for police to use arbitrary stop and search powers against peace protesters and photographers under terrorism legislation.
Kent police is fighting to avoid paying a huge bill for damages to thousands of protesters.
The high court heard that the twins, who cannot be named, and more than 3,500 protesters were herded into airport-style "checkpoints" during the week-long climate camp demonstration at Kingsnorth power station in Kent.
The twins' mother described how her son was left "crying and shaking" and "very pale". She said that he had overheard that protesters had stickers confiscated by police, and feared he would "go to prison" because he had a sticker in his bag. Nothing was taken from their bags.
They were searched under the 1984 Police and Criminal Evidence Act, which requires officers to have a reasonable suspicion that an individual is carrying prohibited weapons that could be used for criminal damage.
At today's hearing, Richard Perks, barrister for the chief constable, said it was now accepted by Kent police that the twins and a veteran environmental protester, David Morris, were unlawfully stopped at the Kingsnorth demonstration in 2008.
Perks added that the chief constable also admitted that unspecified numbers of other climate camp protesters had also been unlawfully stopped and searched.
The twins and Morris, from north London, launched the legal action last year as a test case for the thousands stopped and searched at the demonstration. Kent police have offered to settle in their case but are refusing to admit that thousands of others should be paid damages.
John Halford, the trio's lawyer, said: "Kent police are seeking to buy off these test cases in a desperate attempt to avoid court scrutiny of what amounted to an unlawful frontline policy geared to bring about large-scale breach of civil liberties and protest rights."
Today Perks told the court that Kent police did not admit that they had covertly applied a blanket, unlawful stop-and-search policy at the camp.
There had been a clear and lawful policy, and the huge majority of activists had not been stopped unlawfully. But it was accepted there had been "a misapplication of a clear policy by officers on the ground", he said.
Alex Bailin, barrister for the twins, accused Kent police of failing to obey a court order to disclose documents about the stop and searches. Lord Justice Aikens and Mr Justice Openshaw adjourned the case so that further evidence could be produced.
Last July an official review concluded that the "widescale deployment of stop and search tactics was both disproportionate and counter-productive" at the Kingsnorth demonstration.
It found that fewer than a quarter of the forms recording the reasons for the stop and searches were legible.