Jacqui Smith, the Home Secretary, is under growing pressure to investigate the leaking of new evidence on the killing of the black teenager Stephen Lawrence, just hours before a report criticised the head of the Metropolitan Police for obstructing an inquiry into the Stockwell shooting.
The police were forced to confirm media reports this week that detectives had made a late breakthrough in the 14-year Lawrence case after a newspaper revealed details of a key forensic discovery.
Lawyers acting for the Lawrence family said the timing of the leak raised serious concerns and suggested the police might have deliberately released the information to draw attention away from its beleaguered commissioner, Sir Ian Blair.
The barrister Michael Mansfield QC said he believed it was possible that the news of apparent forensic breakthroughs was released by someone within Scotland Yard to coincide with the publication of a report into the police killing of Jean Charles de Menezes, although he stressed he had no evidence of this.
He said that Stephen's mother, Doreen Lawrence, was "disturbed, dismayed and angered" by this week's press reports, which could jeopardise the investigation into the murder in Eltham, south London, in 1993.
Press reports predicted that five suspects could be rearrested in the light of new forensic evidence which emerged during a review of the case.
The Metropolitan Police later issued a statement that new DNA samples were being taken from individuals as a result of "a forensic opportunity" arising from the use of new technology in the case.
The news broke just hours before the release of the Independent Police Complaints Commission's report into the 2005 shooting of Mr de Menezes by police at Stockwell Tube station in south London, which contained criticisms of Sir Ian for obstructing investigators' inquiries in the immediate aftermath of the death.
Mr Mansfield told the Today programme on BBC Radio 4: "Doreen Lawrence – and no doubt the same would go for [Stephen's father] Neville – is extremely disturbed, dismayed and angered by this kind of publicity." Asked what should be done about the leak, he said: "Stage one has to be – and I think this is where the Home Secretary comes into play – an investigation independent of Scotland Yard as to what has happened here, to establish the facts."
Mr Mansfield said it was vital to establish whether the information had in fact come from police sources.
"It is fairly basic police training that you never broadcast the objectives, the nature, let alone the detail of an investigation, because you jeopardise sources, you jeopardise targets, you jeopardise the nature of the investigation," he said. "The major concern, certainly for Doreen and for Neville, is to ensure the integrity and sanctity of the investigation and to ensure that nothing is said and nothing is done that will jeopardise avenues of future inquiry, because, of course, one doesn't know exactly where it may go."
Under a change in the law it is now possible for a person to be tried twice for the same offence. Judicial safeguards ensure that a second prosecution can only proceed if the evidence is both new and compelling and with permission from the Court of Appeal.
Mr Mansfield suggested that one possible motive for the release of the new information may have been to provide some good news relating to the Met on the day of the IPCC report.
"Assuming just for the moment a police source was responsible for this, one has to say 'Why yesterday [Thursday]?"' he said.
"Yesterday [Thursday] happened to be the day on which the IPCC were going to finally release their Stockwell report on the activities of the Met and the responsibilities of the Met and in particular the blocking of the Stockwell inquiry.
"I think that there is a possibility here that somebody thought, 'Well, we need to offset a bad news day in some way or another and this is a way to at least get on to the agenda that we are making breakthroughs'."