Britain's largest police force stole the identities of an estimated 80 dead children and issued fake passports in their names for use by undercover police officers. The Metropolitan police secretly authorised the practice for covert officers infiltrating protest groups without consulting or informing the children's parents. Over three decades generations of police officers trawled through national birth and death records in search of suitable matches. Undercover officers created aliases based on the details of the dead children and were issued with accompanying identity records such as driving licences and national insurance numbers. Some of the police officers spent up to 10 years pretending to be people who had died. The technique of using dead children as aliases has remained classified intelligence for several decades, although it was fictionalised in Frederick Forsyth's novel The Day of the Jackal. As a result, police have internally nicknamed the process of searching for suitable identities as the jackal run". One former undercover agent compared an operation on which he was deployed to the methods used by the Stasi. The practice was introduced 40 years ago by police to lend credibility to the backstory of covert operatives spying on protesters, and to guard against the possibility that campaigners would discover their true identities. Since then dozens of SDS [Special Demonstration Squad] officers, including those who posed as anti-capitalists, animal rights activists and violent far-right campaigners, have used the identities of dead children.