At least 25 undercover police officers who infiltrated political groups formed sexual relationships with members of the public without disclosing their true identity to them. The total shows how women were deceived on a systemic basis over more than three decades. It equates to nearly a fifth of all the police spies who were sent to infiltrate political movements. Four of the police spies fathered, or are alleged to have fathered, children with women they met while using their fake identities to infiltrate campaigners. One woman, known as Jacqui, has said her life was "absolutely ruined" after she discovered by chance that the father of her son was an undercover officer, more than 20 years after his birth. The officer, Bob Lambert, abandoned them when the son was an infant. The deceptive relationships were a frequent part of intensely secret operations that began in 1968 and lasted more than 40 years. In total, about 139 undercover officers employed in two covert squads " spied on more than 1,000 political groups. Tens of thousands of mainly leftwing and progressive campaigners were put under surveillance. Many of the spies created aliases based on the identities of dead children after searching through archives containing birth and death records to locate suitable matches. The officers typically spent four years pretending to be campaigners while they infiltrated political groups, befriending activists while simultaneously hoovering up information about their protests.