The group was detained on suspicion of conspiracy to commit aggravated trespass and criminal damage at the Ratcliffe-on-Soar power plant, Nottinghamshire Police said.

Police did not provide details about the nature of the threat or the group of protesters. They were taken into custody after a nighttime raid at a primary school near the plant, 190 kilometers northwest of London.

Police said they believed the protests would have posed a serious threat to the safe operation of the power station.

Its owner, German energy company E.On, said the protest 'could have been a very dangerous and irresponsible attempt to disrupt an operational power plant.'

'While we understand that everyone has a right to protest peacefully and lawfully, this was clearly neither of those things,' the company said in a statement.

Environmental groups have previously targeted coal-fired power plants to draw attention to climate change.

In April 2007, 11 members of a group called Eastside Climate Action were arrested after chaining themselves to buildings and equipment on the Ratcliffe site.

Eastside Climate Action said it was not involved in the latest protest. -- AP