Scotland Yard has apologised to seven women who were deceived into "abusive, deceitful, manipulative and wrong" relationships with undercover police officers.
The Metropolitan Police said it has reached a settlement with the women over civil claims relating to the "totally unacceptable" behaviour of a number of officers working for two now disbanded units.
Assistant Commissioner Martin Hewitt said: "I acknowledge that these relationships were a violation of the women's human rights, an abuse of police power and caused significant trauma.
"I unreservedly apologise on behalf of the Metropolitan Police Service. I am aware that money alone cannot compensate the loss of time, their hurt or the feelings of abuse caused by these relationships."
The unprecedented apology and payouts centre on the conduct of officers working for the Special Demonstration Squad (SDS), an undercover unit within Special Branch that existed until 2008, and for the National Public Order Intelligence Unit (NPOIU), which was operational until 2011.
The details of the settlement are being kept secret.
Mr Hewitt said: "Thanks in large part to the courage and tenacity of these women in bringing these matters to light it has become apparent that some officers, acting undercover whilst seeking to infiltrate protest groups, entered into long-term intimate sexual relationships with women which were abusive, deceitful, manipulative and wrong."
The senior officer heard directly from the women involved during a mediation process.
He said: "I wish to make a number of matters absolutely clear.
"Most importantly, relationships like these should never have happened. They were wrong and were a gross violation of personal dignity and integrity."
In his statement, Mr Hewitt said:
The assistant commissioner added that the relationships may well have reflected attitudes towards women that "should have no part in the culture of the Metropolitan Police".
A number of investigations are being carried out into undercover policing, including a judge-led inquiry that opened earlier this year.
Mr Hewitt said: "Even before those bodies report, I can state that sexual relationships between undercover police officers and members of the public should not happen."
Such a relationship would "never be authorised in advance" nor used as a tactic, he added.
Scotland Yard admitted the cases demonstrate failures of supervision and management.
Mr Hewitt said: "By any standards the level of oversight did not offer protection to the women concerned against abuse.
"Undercover policing is a lawful and important tactic but it must never be abused.
"In light of this settlement, it is hoped that the claimants will now feel able to move on with their lives. The Metropolitan Police believes that they can now do so with their heads held high. The women have conducted themselves throughout this process with integrity and absolute dignity."
Set up in 1968, the SDS has been the focus of intense controversy in recent years.
The force also admitted in January this year that the identities of dead children aged up to 17 were used by SDS officers in a practice the Met conceded was "morally repugnant".
A separate police-led Operation Herne found that the unit carried out undercover operations to collect information on 18 justice campaigns over the course of 35 years - including that of Jean Charles de Menezes, who was shot by police after being mistaken for a terrorist.
Home Secretary Theresa May announced that the judge-led public probe would be established after a review found that the squad had spied on the family of murdered teenager Stephen Lawrence.
Press Association
