The extent of the psychological torment of women who became the unwitting lovers of undercover detectives was revealed today in a damning report about covert police tactics.

Four women activists detailed the devastating effect after learning they had fallen in love "with the enemy" in a report detailing the "improper intrusion by the state" into their lives. Their accounts led to a report out today by MPs calling for a fundamental review of legislation governing undercover operations.

The report followed evidence given behind closed doors by Mark Kennedy who had sex with two women while spying on environmental protesters during a 10-year career working undercover.

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Kennedy, who adopted the persona of long-haired dropout Mark "Flash" Stone, denied deceiving the women. "The person that I was seeing, the person that I was sleeping with, was sleeping with Mark Stone," he said.

Five women and one man are suing the Metropolitan Police over alleged intimate relationships with undercover police, including cases where children have been fathered.

Three women, including one of Mr Kennedy's ex-partners, gave evidence in person to MPs on the Home Affairs select committee. Lisa, Kennedy's ex-partner, said: "We are talking about degrading and inhumane treatment. I think what happened to us has been akin to psychological torture." Scotland Yard said yesterday that it expected its £1.2m inquiry into the use of undercover officers to take another three years – despite calls by MPs for it to be completed before the end of 2013.

Operation Herne was launched in October 2011 with more than 30 officers and staff but nobody has been arrested or disciplinary proceedings started.

Committee chairman Keith Vaz said: "The impact of the conduct of undercover officers on the women with whom they had relationships has been devastating, and it represents a wholly improper degree of intrusion by the state into the lives of individuals."

The MPs said detectives should only have sex on assignment in exceptional circumstances and after getting prior permission from senior officers.

Alison's story

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The anti-racist campaigner, who had a five-year relationship with an undercover policeman, told MPs that the couple had 18 months of counselling after disagreeing about having children.

The woman – named only as Alison – said she and "Mark Cassidy" lived as "man and wife" until he disappeared.

She said the realisation he was an undercover officer meant she dropped out of any political activity.

"This is not about just a lying boyfriend… it is about a fictional character who was created by the state and funded by taxpayers' money," she said.

She said she believed "Cassidy" was still a police officer. Scotland Yard declined to confirm or deny anything that might identify anyone who has worked in a covert role.

Caroline's story

An animal rights campaigner told MPs she was having psychiatric treatment after her life fell apart when she learned that her former partner, and father of her child, had been an undercover officer.

The woman – named only as Caroline – said her partner "Bob Robinson" appeared besotted with their son – but she had no idea that he was already married and had children.

He abandoned her in 1987 after orchestrating the breakdown of their relationship, she told MPs in a statement.

He told her he had to flee to Spain after he was involved in the firebombing of a Debenhams store in Harrow.

She said she only learned his identity last year when she saw his photo after Green MP Caroline Lucas named him in parliament as Bob Lambert.