The revelations have exposed a lack of rules for officers on undercover assignments.
Kennedy spent seven years posing as long-haired dropout climber Mark “Flash” Stone, associating with green campaigners accused of planning to invade Ratcliffe-on-Soar power station near Nottingham.
The assignment very publicly collapsed in January last year.
Chief Constable Jon Murphy, the leader on organised crime for police chiefs, described Kennedy’s alleged fraternising as “morally wrong” and “grossly unprofessional”.
However, there appears to be no explicit ban on sexual interaction the Association of Chief Police Officers (Acpo) said.
Kennedy’s error in judgement emerged as Her Majesty’s Inspectorate of Constabulary (HMIC) published the findings of a review, which called for tougher control of undercover assignments.
The watchdog said as it stands, the code for undercover officers states “that conduct must still be consistent with the spirit of the regulations and with the fundamental aims of the respective organisation”.
The HMIC review called for a new system where any long-term undercover operation must first be approved by the independent Office of Surveillance Commissioners (OSC).
The report stressed that undercover officers have helped prevent bomb attacks and seize weapons from extremists.
However, they only needed approval by an assistant chief constable while police “planting a bug” needed the go-ahead from the Home Secretary.
They are also less accountable because they are gathering intelligence rather than evidence that must stand up in court.
The HMIC review was ordered after questions were raised about Kennedy’s costly operation.
The case against the green campaigners collapsed after they claimed an undercover officer offered to give evidence on their behalf.
The HMIC report found Kennedy became “resistant to management intervention”.
Main images: Getty