The home secretary is considering ordering a new public inquiry into the murder of Stephen Lawrence, the Guardian has learned.
The prospect of a new Macpherson-style inquiry ? the original report published in 1999 made landmark findings against the police ? has been triggered by allegations that police corruption may have shielded the gang that murdered Lawrence in a racist attack.
Theresa May sees the allegations as being of the "utmost importance" which must be investigated thoroughly to avoid undermining confidence in the police .
Doreen Lawrence has called on the home secretary to order a second public inquiry into the police investigation of the murder of her son, who was killed by a racist gang 19 years ago, on April 22, 1993.
The call for a "Macpherson 2" comes as the Metropolitan police says it has been unable, after a month of investigating, to establish whether it passed potentially crucial files detailing investigations by its anti-corruption command to the public inquiry into Lawrence's death, which was held in 1998.
Home Office officials have pressed the Met over a report in the Guardian last month revealing that a secret Scotland Yard report detailing questions about the conduct and integrity of a police chief involved in the Stephen Lawrence case was not given to the inquiry.
Former Met commander Ray Adams was questioned at the Macpherson inquiry about corruption. But neither the Lawrence family nor the inquiry panel were given a report by Scotland Yard containing the intelligence and findings of an investigation by its anti-corruption command.
The investigation, codenamed Operation Russell, raised questions about Adams's conduct in the years before the Lawrence case, informed sources say, while finding insufficient evidence to bring criminal charges. Adams insists it exonerates him and told the Guardian he denies any wrongdoing.
The Met's investigation into Adams began in April 1987, by which time he had risen to become the Met's head of criminal intelligence, in charge of gathering information about major criminals and criminal networks. It ended with no criminal or misconduct charges being brought against Adams but lists concerns about him, in one instance describing his conduct as highly questionable and unprofessional.
The investigation was carried out by the Met's complaints investigation bureau. It was triggered by allegations that Adams had taken bribes from criminals and had improper relationships with criminal informants, which he strenuously denied. Some of the allegations against Adams centred on his relationship with the subsequently convicted murderer Kenneth Noye.
At the Macpherson inquiry the Lawrence lawyers claimed Noye had a criminal associate, Clifford Norris, whose son, David Norris, was a prime suspect in the murder of Lawrence. David Norris ? along with Gary Dobson ? was finally convicted in January this year of the murder.
Macpherson found no evidence of wrongdoing against Adams, but Mrs Lawrence says the claims that potentially crucial material was kept from the inquiry means that finding must be revisited.
Mrs Lawrence said: "The revelations in the Guardian throw Macpherson's conclusions about corruption completely into doubt and justify my longstanding suspicions.
"This gives further impetus to my demand to the home secretary for a public inquiry into corruption. I cannot see how Theresa May can now refuse. Not only must a new public inquiry look at whether corruption existed in the police investigation but why it was that such critical information was kept from us ? Stephen's family".
In the five weeks since the article was published the Met has been unable to say if it passed the files to Macpherson. The Met said it has started its own inquiry: "The Deputy Commissioner is overseeing enquiries to establish paperwork relating to investigations into corruption that have been linked to the Stephen Lawrence murder investigation. Should any new information arise it would be seriously considered."
Mrs Lawrence called on the Met to come clean: "The new commissioner has a choice to make; he can be open and transparent, or be tarred by the same brush of the past. We want to know what is in the file, and what other material the Met has about officers whom we suspected at the Macpherson inquiry."
Several MPs as well as London mayor Boris Johnson have supported calls for a new inquiry into corruption.
Within weeks of the murder convictions earlier this year, the issue of corruption in the Lawrence case surfaced when the Independent made allegations about a detective in the Lawrence case, former detective sergeant John Davidson. The allegations about Davidson and the Lawrence case were also previously made in the Guardian in 2002 and by the BBC in 2006. Davidson denies any wrongdoing.
An IPCC investigation in 2007 found no evidence to substantiate allegations that a supergrass passed information about Davidson's alleged corruption in the Lawrence case to Scotland Yard, who then buried it.
The concerns around former commander Adams and whether the Met passed information to the Macpherson inquiry about its investigations into him, may be the more likely of the two sets of allegations to increase the pressure on the home secretary to act.
Factors against May ordering a new public inquiry include cost, and whether it would be the best forum to explore such issues. Factors in favour of an inquiry include the seriousness of the allegations and the fact they have not gone away, plus the fact a threshold for a public inquiry is relatively low. The Inquiries Act 2005 states that an inquiry should be held if "particular events have caused, or are capable of causing, public concern".