The Guardian newspaper says that London's Metropolitan Police Service stole the identities of dozens of dead children to use as aliases for undercover officers, mining those children's personal histories to build covers and even issuing fake passports in their names.
The allegation is another potential embarrassment for Scotland Yard's undercover program, which has previously been rocked by revelations that police spies had sex with their targets and fathered children with activists under surveillance.
It wasn't exactly clear how long or often the police used the dead children's identities. The Guardian said it had seen a document suggesting that around 80 officers used such identities between 1968 and 1994, but said that one case may be as recent as 2003.
Police said in a statement on Monday that they had received a formal complaint about the practice and "appreciate the concerns." The practice "is not something that would currently be authorized," they said.
Stealing the identities of dead people is a classic piece of spycraft and features prominently in Frederick Forsythe's famed 1971 thriller "The Day of the Jackal."
But lawmakers and law enforcement officials were left wondering on Monday whether taking on the identity of a dead child was an appropriate technique for British police. Opposition lawmaker Keith Vaz told Sky News television "that the parents of those involved should be informed immediately."
The Guardian, which has run a series of stories exposing the seamy side of Scotland Yard's undercover work, based its story on detailed accounts provided by two undercover officers - neither of whom it identified by name - and an ex-girlfriend of a third one, who was identified with a pseudonym.
The newspaper said all three men were members of Scotland Yard's Special Demonstration Squad, which was disbanded in 2008.
One of them, the newspaper said, assumed the identity of an eight-year-old boy who died of leukemia in 1968 - going so far as to assume the boy's hometown and even his parents' names when he infiltrated an anti-capitalist group in the 1980s. The officer was found out when he left his girlfriend - part of the group he was spying on - and she pulled up his vital records in an effort to track him down.
The newspaper described her horror when she realized that the person her boyfriend was pretending to be had died 25 years ago.
Former director of public prosecutions Ken Macdonald said that the latest revelation, coupled with past reporting about undercover officers fathering children with their targets, suggested a police force gone wrong.
"How are you supposed to maintain a level of fair and objective evidence-gathering if you are having sex with the person you are targeting, fathering a baby and then abandoning it, using a dead child's identity?" he said in an interview with BBC radio.
"These are all examples of areas in which the police have completely lost their moral compass and have completely failed to understand the boundaries," he said. "We don't know quite how these units were operating in days gone by. It looks as though they've effectively gone rogue."