A former police boss who controversially met an undercover officer during the Stephen Lawrence inquiry would have faced disciplinary proceedings if he had not been allowed to retire.
Watchdog the Independent Police Complaints Commission (IPCC) said ex-Metropolitan Police Commander Richard Walton "would have had a case to answer for misconduct" if he was still a serving officer.
In January, lawyers for Stephen's father, Neville Lawrence, made a last-ditch, and unsuccessful, attempt to stop Mr Walton retiring so that he could face misconduct claims.
Mr Walton was temporarily moved from his job leading the force's counter-terrorism command in 2014, following the publication of a damning report by barrister Mark Ellison QC into the original Lawrence murder investigation.
Mr Ellison revealed that an undercover officer - known as N81 - held a meeting in 1998 with Mr Walton, who was then an acting detective inspector working on Scotland Yard's Lawrence review team, responsible for making submissions to the Macpherson Inquiry, the probe into the appalling failures in how the 18-year-old's racist murder was investigated.
Mr Walton was alleged to have met the undercover officer and ''obtained information pertaining to the Lawrence family and their supporters, potentially undermining the (Macpherson) inquiry and public confidence".
It was also claimed that he provided inconsistent accounts to Mr Ellison's review team.
It has previously been claimed that N81 told Mr Walton that Stephen's parents had separated, although the IPCC found no evidence of this.
The watchdog said four officers, including former undercover officer Bob Lambert and ex-commander Colin Black, had potentially "played a part" in arranging the meeting.
It found that Mr Lambert, who left Special Branch in 2007, would have had a case to answer for misconduct, but that Mr Black and the other two officers would not.
While Mr Walton would have faced proceedings over the meeting, he would have faced no action over claims that he provided inconsistent accounts to Mr Ellison's team, the IPCC said.
IPCC deputy chairwoman Sarah Green said: "During the Stephen Lawrence Inquiry, the honesty and integrity of the Metropolitan Police was rightly under intense public scrutiny. The force's reputation may have suffered immense damage had the meeting become public knowledge at the time.
"The IPCC found that Robert Lambert and Richard Walton both had a case to answer for discreditable conduct in that their actions could have brought the force into disrepute. As neither of the men are now serving police officers, it is not possible for misconduct proceedings to take place to determine whether or not the case would be proven."
Neville Lawrence called for Lord Justice Pitchford's public inquiry into undercover policing to look at the chain of command above Mr Walton.
In a statement through his lawyers, Hodge Jones & Allen, he said: "The IPCC report makes it clear that my family were wrongly spied upon by police during the Macpherson Inquiry in 1998.
"I am glad that they have made findings of a case to answer for misconduct; however, the Pitchford Inquiry now needs to look into this matter in more detail and to find out at what level of seniority within the Metropolitan Police this spying was sanctioned.
"I have made no secret of the fact that I think it is wholly wrong that former Commander Walton was so recently allowed to retire and will avoid the disciplinary process he should have faced.
"I have long felt that allowing officers to retire to avoid disciplinary action totally undermines public confidence in the police. The police and the IPCC should have ensured that this investigation was concluded in good time to ensure that former Commander Walton could not have avoided disciplinary proceedings.
"In my 23 years of experience of the Metropolitan Police, it has often been evident that had they been open about misconduct then it could have saved everybody a lot of heartache over the years.
"However, I see no sign that they are taking a more open approach to the inquiry as they are currently seeking to persuade the inquiry to restrict public access to information and rely on a policy of neither confirming nor denying whether an individual was an undercover police officer."