Terror legislation was used to stop a British climate change activist from travelling to Denmark, it has emerged.
Chris Kitchen, 31, said he was prevented from crossing the border on Tuesday at about 5pm when the coach he was travelling on stopped at the Folkestone terminal of the Channel Tunnel.
Mr Kitchen told the Guardian that police officers boarded the coach and, after checking all passengers' passports, took him and another climate activist to be interviewed under schedule 7 of the Terrorism Act 2000, a clause which enables border officials to stop and search individuals to determine if they are connected to terrorism.
He was asked what he intended to do in Copenhagen and also about his family, work and past political activity.
Mr Kitchen said he pointed out that anti-terrorist legislation did not apply to environmental activists but said the officer replied that terrorism "could mean a lot of things".
His coach had left by the time his 30-minute interview had finished and police paid for a ticket for him to return to London.
Mr Kitchen said he believed the officials knew his name and had planned to remove him before they boarded the coach as passports were not initially scanned.
"The use of anti-terrorist legislation like this is another example of political policing, of the government harassing and intimidating people practising their hard earned democratic rights," he told the Guardian.
"We are going to Copenhagen to take part in Climate Justice Action because we want to protest against false solutions like carbon trading and to build a global movement for effective, socially just solutions.
"People who are practising civil disobedience on climate change in the face of ineffectual government action are certainly not terrorists, and I am sure that their actions will be vindicated by history."
Mr Kitchen said he would make a second attempt last night to get to Denmark.
Once there, he plans to take part in discussions organised by a network of protest groups coming together under the banner Climate Justice Action in the run-up to the United Nations summit.
Friends of the Earth's head of climate Mike Childs said: "It's outrageous to stop someone from travelling to Copenhagen to protest on climate change.
"Climate change is a global crisis that will have catastrophic consequences unless world leaders take drastic action to tackle it, so it's not surprising people want their voices to be heard.
"The police should be supporting people's right to protest peacefully.
"One of the most effective ways to campaign is to unite as many voices as possible at the same time and this is exactly what Friends of the Earth will be doing in Copenhagen in the coming weeks."
A Home Office spokesman said: "There has been no change in policy.
"Schedule 7 of the Terrorism Act 2000 enables an examining officer to stop, search and examine a person at a port or in a border area to determine whether they are someone who is or has been concerned in the commission, preparation or instigation of acts of terrorism.
"The exercise of the powers by the police is an operational matter for each force."