The existence of a squad of police officers sent deep undercover in political groups was so top secret that many of the UK's most senior officers were completely oblivious until they began reading reports in the Guardian 10 years ago. When Lisa Jones ... and her friends established that [her boyfriend Mark] Kennedy was a police officer who had been spying on climate change activists, the story [collapsed] a major trial ... quashing the convictions of environmental activists who had been prosecuted for conspiring to shut down one of the UK's biggest power stations. The police spies initially belonged to the Special Demonstration Squad (SDS), which was created to control the restive protests of the late 1960s, including those opposed to the war in Vietnam, but continued to monitor protest groups for a further four decades. Their deployments typically lasted four to five years, with officers living alongside political campaigners, forming deep bonds of friendship, or romantic liaisons, with their targets. At least three of the police spies fathered children with women they met while undercover. Over more than four decades, at least 139 police officers were given fake identities to closely monitor the inner workings of more than 1,000 political groups. These police spies were tasked with gathering intelligence that could be used to disrupt and monitor political groups. Their targets included the black power movement, the anti-apartheid campaign, leftwing groups, and anarchists. Many ... were instructed by their superiors to adopt the identities of dead children to lend credibility to their aliases " with some, in a macabre ritual, even visiting the graves of the deceased children whose identities they were using. One of the most notorious police spies, Bob Lambert, who adopted the identity of a seven"year-old boy who had died of a congenital heart defect in 1959.