The former Director of Public Prosecutions said police appeared to have "completely lost their moral compass" after a report emerged about officers using the IDs of dead children.
Lord Macdonald, who has called for a pubic inquiry, told the BBC Radio 4 Today programme:
A document seen by the Guardian indicated around 80 police officers used the identities of dead children between 1968 and 1994, the paper reported.
The practice was allegedly adopted to lend credibility to officers working undercover and provide them with a back story while spying.
John O'Connor, a former head of the Flying Squad, has told Daybreak that the police "have been arrogant and stupid for using the identities of dead children."
A policeman who was given the identity of a dead four-year-old boy said he felt he was "stomping on the grave" of the child.
The officer adopted the fake persona of Pete Black while undercover in anti-racist groups, the Guardian reported.
He told the paper: "A part of me was thinking about how I would feel if someone was taking the names and details of my dead son for something like this."
Another officer, who used the identity of a child car crash victim, said he was conscious the parents would "still be grief-stricken" but argued his actions were for the "greater good".
Both officers worked for the Special Demonstration Squad (SDS), which was apparently disbanded in 2008.
Scotland Yard has confirmed that a complaint has been received over reports that the Metropolitan Police gave the IDs of dead children to undercover officers infiltrating protest groups:
Undercover police officers working for Britain's largest force used the identities of dead children and issued fake passports in their names, reports the Guardian.
The Metropolitan Police authorised the practice for covert officers infiltrating protest groups without consulting or informing the children's parents, the newspaper said.
Over three decades, generations of officers reportedly went through national birth and death records in search of suitable matches.
Officers were then given aliases and issued with official documents such as driving licences and national insurance numbers.
Last night, Scotland Yard said the practice was not "currently" authorised.
Undercover police officers have allegedly used the identities of dead children and issued fake passports in their names. Daybreak's Richard Gaisford reports.
Keith Vaz, the chairman of parliament's home affairs select committee has said he was shocked at the "gruesome" practice.
He told the Guardian: "It will only cause enormous distress to families who will discover what has happened concerning the identities of their dead children."
- Another officer said he was conscious the parents would "still be grief-stricken" but argued his actions could be justified because they were for the "greater good".
- Both officers worked for the Special Demonstration Squad (SDS), which was apparently disbanded in 2008.
- A document seen by the newspaper indicated around 80 officers used such identities between 1968 and 1994, it was reported.