A former spy is suing the Metropolitan police for failing to "protect" him from falling in love with one of the environmental activists whose movement he infiltrated.

Mark Kennedy, who was known as Mark Stone until the activists discovered his identity in late 2010, filed a writ last month claiming damages of between £50,000 and £100,000 for personal injury and consequential loss and damage due to police "negligence".

"I worked undercover for eight years," he told the Mail on Sunday. "My superiors knew who I was sleeping with but chose to turn a blind eye because I was getting such valuable information They did nothing to prevent me falling in love."

Kennedy says since he was unmasked he has been diagnosed as suffering from post-traumatic stress syndrome. His wife, Edel, has filed for divorce, and is seeking compensation for "emotional trauma".

"When my cover was blown it destroyed my life. I lost my job, my girlfriend and my reputation," he said. "I started self-harming and went to a shrink who diagnosed me with post-traumatic stress syndrome. The blame rests firmly at the feet of my superiors at the Met, who had a duty to protect me."

Ten women and a man are also suing the Met for emotional trauma, saying they were duped into having sex with undercover officers. Three of the women are former lovers of Kennedy. It is one of these women whom the ex-spy claims to have fallen in love with.