Scotland Yard was under pressure tonight to explain whether it had authorised an undercover officer to have sexual relationships with environmental activists after a woman came forward to say she felt violated following a close relationship with the man unmasked this week as a police spy.

The woman told the Guardian that Mark Kennedy, the Metropolitan police officer at the centre of a growing controversy over the infiltration of peaceful environmental protest groups, had relationships with several women and may have used sex as a tactic to glean intelligence.

"He had so many friends and relationships with people in the movement that I'm questioning whether this was a tactic – or part of his task – to become more trusted or respected within the scene," she said today. "In a general sense, there is the feeling that if somebody was being paid to have sex with me, that gives me a sense of having been violated."

Following questions in parliament over the Kennedy case, a member of the Met's watchdog called tonight for a review into the conduct and handling of the officer known to activists as "Mark Stone", who spent seven years living among individuals campaigning against climate change.

"There should be guidance so officers remain focused on what they are doing," said Cindy Butts, a member of the Metropolitan Police Authority.

"I don't think 'by any means necessary' should be the modus operandi [for undercover officers] at all. There should be a review. I expect questions on all aspects of this case, including these [sexual] allegations."

The woman who said she had had a sexual relationship with Kennedy wants to be known only by her first name, Anna. She said she had sex more than 20 times with the undercover officer about five years ago, including at his house in Nottingham, when she was aged just 21. They met at protests around Europe, and it seemed clear to her that Kennedy was "seeing other women" around the same time. "I'm not sure personally if I would be willing to take part in an inquiry that touched on our sexual relationship," she said. "If the Met knew that this was going on, then obviously they should reveal this. There should be an inquiry into whether this is legal."

Kennedy, who joined the police in about 1994, is known to have had a wife and children before going undercover. There have also been unconfirmed reports that Kennedy had a long-term relationship with a woman in Nottingham while posing as an activist.

Questions over the ethics of the Kennedy operation have already been raised in Germany, where the MP Andrej Hunko has tabled questions asking whether authorities authorised the undercover officer to have "sexual relationships" in the country.

A Guardian investigation revealed on Monday that Kennedy had used a fake passport to travel to 22 different countries while posing as a campaigner, earning the trust of activists and feeding back intelligence to his commanders.

Confronted in October about his real identity by friends, Kennedy confessed, and has since expressed remorse. He had quit the Met several months earlier. "I hate myself so much I betrayed so many people," he recently told an activist friend. "I don't want this ever to happen to anyone ever again. What's happened is really wrong."

In an apparent attempt to seek redemption, Kennedy offered to assist six campaigners who had been due to face trial this week for conspiring to invade a power station near Nottingham. The trial collapsed on Monday after allegations emerged of Kennedy having acted as an agent provocateur ahead of the demonstration.

No police force or oversight body has yet commented on Kennedy's case, and it is not known whether the Met or the National Public Order Intelligence Unit, a monitoring agency he had been seconded to, condoned or even knew about his sexual activity.

However, two of Britain's most senior police officers told parliament today that conduct of undercover police officers was supervised and subject to oversight. Responding to questions from the home affairs select committee, Peter Fahy, chief constable of Greater Manchester Police, said: "It is something that is very tightly controlled and it does play an enormous contribution in some very, very difficult investigations."

He added that Kennedy's case, in which the officer appeared to have "swapped sides", was unusual. "Because it is so well managed and tightly controlled and there is a lot of concern about the welfare of these officers this sort of thing we have had over the last couple of days is extremely, extremely rare."

Chris Sims, chief constable of West Midlands Police, said it was too early to comment on the details of the case, but added that in general it was crucial to ensure that the "line is not crossed between infiltration to gather intelligence and the agent provocateur role which is absolutely not part of the system".

Kennedy is living abroad. His unmasking has prompted consternation among protesters, especially since Kennedy told activists friends he was "not the only one – by a long shot".

Activists are known to now be suspicious about two individuals – a man and a woman – who mysteriously disappeared from their movement over the last decade.

Today Melissa Jacob, an activist giving a statement on behalf of climate campaigners, said: "This case gets more murky every day. Did PC Kennedy have sexual relations with Anna to obtain information for the British state? If so, then this looks like state-sponsored sex abuse.

"The Met really cannot stay silent on the role of undercover officers in policing protest. How many more PC Kennedys are there in our movement?"