LONDON — They lived together, travelled abroad on vacation and, for five years, behaved like any other couple. Then one day the man, who called himself Mark Cassidy, disappeared, leading his bewildered ex-partner to eventually discover that she had been living with a married police spy.

The case is one of seven that prompted a formal apology from the British police yesterday (Nov 20) for the behaviour of undercover officers who used relationships — one nine years long — to gather intelligence and to infiltrate environmental, social justice or other advocacy groups.

In doing so, the men had engaged in “long-term, intimate, sexual relationships with women which were abusive, deceitful, manipulative and wrong,” Mr Martin Hewitt, assistant commissioner of the Metropolitan Police, said in a statement.

Offering an unreserved apology, Mr Hewitt said that the women were “deceived, pure and simple”, adding that “these relationships were a violation of the women’s human rights, an abuse of police power and caused significant trauma”.

The cases have revealed the extraordinary lengths to which the British police went to get information about the activities of a range of activist groups from the mid-1980s until about 2010.

The police admission of “failures of supervision and management” came at the end of a four-year legal action that ended with “substantial” damages being accepted by the seven women. Another woman is still contesting her case against the police, according to lawyers for the victims.

In another case, settled last year and involving an undercover officer who had fathered a child, a compensation payment of 425,000 pounds (S$911,880) was made, according to the British news media.

The police officers involved worked for a group called the Special Demonstration Squad, which was disbanded in 2008, and for another unit called the National Public Order Intelligence Unit, which operated until 2011.

In a joint statement, the seven women said that no apology or financial compensation could “make up for what we and others have endured”, but that they were “pleased the police have been forced to acknowledge the abusive nature of these relationships and that they should never happen”.

The statement added that “the level of deception perpetrated by state agents seeking to undermine movements for social change is more akin to that of the Stasi in East Germany”.

Evidence given by some of the victims to Parliament in 2013 underlined the personal cost to those who were left searching for answers after their partners disappeared, only to discover that they had been tricked into relationships and then betrayed.

One woman described how she looked for her partner after his disappearance, only to discover a death certificate with the name he had been using. It proved to be for a child who had died of leukaemia at the age of 8, suggesting that the police had used identities of the deceased.

Having been granted legal anonymity, and giving evidence under the pseudonym of Alison, the woman who had the five-year relationship with “Mark Cassidy” said the deception had caused her to question her own judgement and damaged her ability to trust others.

“It has also distorted my perceptions of love and my perceptions of sex, and it has had a massive impact on my political activity,” she said.

“I met him when I was 29, and he disappeared about three months before I was 35,” she told lawmakers. “It was the time when I wanted to have children, and for the last 18 months of our relationship he went to relationship counselling with me about the fact that I wanted children and he did not,” she said.

In a statement yesterday she added that she had “later discovered he was married with children throughout this time”.

“I loved him very deeply and have suffered significant psychological damage from the experience of suspecting and then proving he was an undercover police officer,” she said. NEW YORK TIMES