One of the country's most senior police officers has refused to apologise to the parents of dead children whose identities have been allegedly used by undercover cops.
Metropolitan Police deputy assistant commissioner Patricia Gallan told MPs she understood concerns but had to uncover the truth before she said sorry.
Addressing the Home Affairs Select Committee, Ms Gallan said Scotland Yard has received two complaints that a dead child's details were stolen by undercover cops - but admitted the parents involved had not been informed.
And she revealed that £1.25 million had been thrown at the investigation into the conduct of undercover police within the potentially rogue Special Demonstrations Squad (SDS) at the centre of the allegations.
Ms Gallan said 20 police officers and 11 staff were working on Operation Herne, the inquiry into the actions of the SDS - a unit set up in 1968 to infiltrate subversive political groups.
The team is wading through more than 50,00 documents as it investigates claims that officers formed sexual relationships with the people they were spying on, as well as allegations that dead children's identities were assumed.
She said: "At some point it will fall upon this generation of police leaders to account for the activities of our predecessors but at the moment we must focus on getting the truth."
Asked by Committee chairman Keith Vaz if she was "shocked" by reports that up to 80 officers had taken part in the practice, Ms Gallan said she could not confirm whether the numbers were accurate.
She said: "I've seen evidence of one case and very recently received a complaint of a second case and that's being investigated.
"I think more evidence will come to light of this practice. I'm very concerned by what I'm hearing and I do recognise people will be upset by what they've heard."
She added that the practice was currently "not sanctioned" within the Met Police, nor any other force in the country.
Asked by Mr Vaz if the parents of the dead children allegedly involved should be informed, Ms Gallan said: "I think it's important that we find out all the circumstances and find out if it's actually accurate. We wouldn't want to cause more hurt to anyone involved. We need to get to the accuracy of it."
Ms Gallan said the practice was confined to two units - the SDS within the Met and The National Public Order Intelligence Unit - which was set up in 1999 to track green activists.
Mr Vaz pressed the deputy assistant commissioner for an apology to the parents whose children may be involved.
But she said: "I've got to examine all the evidence, keep an open mind and at the appropriate time statements will be made.
"I do absolutely appreciate the concerns. I do understand the upset and why people are very distressed but until I know all the facts you're asking me to get ahead."
Mr Vaz said: "I'm disappointed that you've not used the opportunity to be able to send out a message to those parents who have children who may have had their identity being used that the Met is actually sorry that this has happened.
"But also you've known about one case since September and despite the fact we've spent £1.25 million, and you have 30 officers and staff working on the case, you still haven't go to the bottom of why this dead child's identity has been used."
Earlier in the session, Ms Gallan was asked if she thought it was possible for undercover police to carry out their duty without having to form sexual relationships.
She said: "I don't believe you can authorise such activity. I know the law is silent on the matter but morally I'm absolutely clear such activity should not be authorised or sanctioned."
Earlier in the session, the Committee took evidence from lawyers representing a number of women who claim they were duped into relationships with undercover officers.
Some of the claimants say they had relationships with Mark Kennedy, the undercover police officer who spent seven years spying on environmental activists posing as long-haired dropout climber Mark "Flash" Stone.