I'm not particularly surprised that the cops used the identities of dead children to establish their 'legends' while infiltrating protest groups. We should expect stealing the identities of dead children to be among the range of processes that infiltrating protest groups actually involves. I suspect as well that there was some urge among the people involved to convince themselves that they were real, proper secret agents rather than undercover cops out on a spree.
This gave me pause though:
During his covert deployment, Dines had a two-year relationship with a female activist before disappearing from her life. In an attempt to track down her disappeared boyfriend, the woman discovered the birth certificate of John Barker and tried to track down his family, unaware that she was actually searching for a dead child.
She said she was relieved that she never managed to find the parents of the dead boy. "It would have been horrendous," she said. "It would have completely freaked them out to have someone asking after a child who died 24 years earlier."
I really hope Ian McEwan isn't reading this and dashing an email off to his publisher...