Former MI5 agent says he had panic attacks
A former MI5 spy has broken cover to give the BBC an unprecedented account of his life in service - and describe his anger at the way he was treated.
The agent, whose codename was Robert Acott, said he worked undercover for 18 years, mostly following Islamic and Irish terrorist suspects.
He says MI5 pushed him out after he suffered symptoms of stress, later diagnosed as PTSD. MI5 said it would not comment on the claims. However, security sources said they felt this was one side of the story. Here he speaks to Newsnight's Nick Hopkins.