Undercover policeman Mark Kennedy 'upset' by accusations of state-sanctioned abuse
Undercover cop Mark Kennedy lived a double life, infiltrating environmental protest groups as 'Mark Stone' and reporting information back to his police handlers.
The married policeman also had a serious relationship with one of the protesters.
In an exclusive in-depth interview, Kennedy told BBC Radio 5 live: "I spent many, many hours with [the protesters] every day."
"I met this person and it happened," Kennedy explained to Victoria Derbyshire. "It's upsetting, yeah."
You can hear other BBC Radio 5 live highlights by visiting the Best Bits section on the website.
Victoria Derbyshire broadcasts Monday - Friday 1000 - 1200 on BBC Radio 5 live.