MPs have raised serious concerns about the use of undercover policing - saying they could be infiltrating the lives of ordinary members of the public.
The influential Home Affairs Committee called for an urgent review of the law, pointing to examples of unacceptable sexual relationships and "ghoulish" use of dead children's identities by undercover cops.
The tactic came under the spotlight in 2011 when former PC Mark Kennedy was unmasked as an undercover officer who spied on environmental protesters as long-haired dropout Mark "Flash" Stone and had at least one sexual relationship with one of the activists.
Five women and one man are suing the Met Police over alleged intimate relationships with undercover police, including cases where children have been fathered.
It has also been reported that one officer planted a bomb on behalf of an animal rights group and that another was prosecuted under his assumed persona.
Committee chairman Keith Vaz MP said: "We are not satisfied that the current legislative framework provides adequate protection against police infiltration into ordinary peoples' lives - a far more intrusive form of surveillance than any listening device or hidden camera."
The MPs called for a lengthy Met Police investigation into possible misconduct to be completed as soon as possible, and said police chiefs should be stripped of their role in setting standards for covert policing.
They said the terrible impact on the women's lives was "beyond doubt" with "risk to their psychological well-being", adding "there are some lines police officers must not cross".
In its interim report, the committee called for an urgent review of the Regulation of Investigatory Powers Act (Ripa) as there
Future guidance on undercover operations should make it clear "beyond doubt" that it is not acceptable for children to be raised by undercover police through operational duties, it said.
It has also been claimed that undercover officers used dead children's identities to build cover stories by "borrowing" the deceased's name, date of birth, parents' identities and creating a false back-story including the schools they attended.
The committee demanded that all families involved should be informed immediately, after it emerged this had not been done
by the Met Police.
The report said: "The practice of 'resurrecting' dead children as cover identities for undercover police officers was not only ghoulish and disrespectful, it could potentially have placed bereaved families in real danger of retaliation.
"The families who have been affected by this deserve an explanation and a full and unambiguous apology from the forces concerned.
A Home Office spokesman said undercover policing was a vital element of the fight against organised crime and terrorism, but added it was crucial for covert powers to be used proportionately and with effective safeguards.