Police Shagging Targets while undercover.
Police used sex as a tool during undercover operations while tactical "promiscuity" was viewed as "part of the job", according to a former agent.
The officer, who worked in a special unit of the Met Police for four years, said sexual relationships with activists were common among those gathering intelligence from anarchist, left-wing and environmental groups.
His claims, made to The Observer, contradict comments made last week by the Association of Chief Police Officers (Acpo) which insisted the practise was forbidden.
But the former officer, once a member of the Special Demonstration Squad (SDS), a covert unit formed to prevent violent disorder on the streets of London, said sex helped to maintain cover.
He has admitted to sleeping with at least two of his female targets for information.
"Everybody knew it was a very promiscuous lifestyle," he is quoted as saying. "You cannot not be promiscuous in those groups. Otherwise you'll stand out straight away."
The unnamed officer claimed there was no set of instructions dictating whether officers could or could not have sex with activists.
Among undercover police it was "basically just regarded as part of the job. It'd be highly unlikely that you were not [having sex]".
Sometimes officers would use sex to help maintain their cover or "glean more intelligence - because they certainly talk a lot more, pillow talk".
The officer, who infiltrated anti-racist groups between 1993 and 1997, said falling in love could jeopardise an investigation and was regarded as unprofessional.
His revelations follow the controversy surrounding former Met officer Pc Mark Kennedy who monitored the actions of protesters across Europe under the guise of a long-haired, drop-out climber called Mark Stone.
The case against six demonstrators accused of conspiring to shut down Ratcliffe-on-Soar power station collapsed earlier this month after he offered to give evidence on their behalf.
In a newspaper interview Acpo spokesman Jon Murphy said sexual relationships for the purpose of intelligence gathering was "grossly unprofessional" and "absolutely not authorised".
"It is never acceptable for an undercover officer to behave in that way," he added.
Three separate police investigations are being carried out following the revelations about Mr Kennedy.