Green MP Caroline Lucas told a court yesterday that a fear of being "haunted" by guilt for failing to stop fracking inspired her to join the Balcombe blockade.

Ms Lucas and her son were among 30 activists snatched by police during a sit-down protest on a road to a fracking site in Sussex last August.

She has been on trial with four other activists charged under the Public Order Act since Monday.

At Brighton magistrates' court she passionately defended her decision to join the protest and ignore police requests to move.

"It felt important to serve the right to peaceful protest," she told the court.

"I'm haunted by the idea that my children and my children's children will turn round to me and say: 'What did you do about this overwhelming threat?'

"And I want to do all I can do peacefully to address that before it's too late."

Ms Lucas also revealed how she became distressed after seeing her son forcefully dragged off and arrested by cops at Balcombe.

The pair were sitting in a circle in the road and holding hands when police officers swooped on them.

She said: "I was aware that the police tactics looked disproportionate."

"I was aware that my son was in pain and I was very upset about it.

"If we had had another 10 to 15 minutes we could have come to an agreement to end it and dispersed. We weren't doing anything different than we were in the previous five hours."

Police were heavily criticised for using painful pressure point techniques to wrench activists from peaceful protests.

But the Brighton Pavilion MP insisted it was important to join the Frack Off protest camp because it was "at the front line of this whole new fossil fuel industry."

She insisted the action outside its main entrance was a "legitimate" and "appropriate" way of sending a message to fracking enthusiasts in the Con-Dem government.

"If this protest hadn't been effective it would have been made harder to persuade the government to stop fracking and go down cleaner energy routes," said Ms Lucas.