There is evidence to suspect one of the detectives on the original Stephen Lawrence murder investigation acted corruptly, a major review has found.

There was a high level of suspicion that former Detective Sergeant John Davidson was corrupt both before and after he worked on the police investigation, a report by Mark Ellison QC says.

And there are still lines of inquiry that may be capable of providing evidence of corruption among other officers, although that evidence does not currently exist, the review adds.

Stephen, 18, a would-be architect, was stabbed to death by a group of up to six white youths, in an unprovoked racist attack as he waited at a bus stop in Eltham on April 22 1993. It took more than 18 years to bring two of Stephen's killers to justice.

Mr Ellison QC, who was commissioned by the Home Secretary to conduct the review, successfully prosecuted Gary Dobson and David Norris for Stephen's murder in 2012.

The Ellison report says that, in late July 1998, Scotland Yard's Anti-Corruption Command held a debriefing with former Detective Constable Neil Putnam, in which he made claims against Mr Davidson.

The barrister says that both the intelligence picture suggesting Mr Davidson was a corrupt officer and the content of Mr Putnam's debriefing should have been revealed to the public inquiry led by Sir William Macpherson.

"It is a source of some concern to us that nobody in the MPS who was aware of the detail of what Neil Putnam was saying about Mr Davidson appears to have thought to ask him about Mr Davidson's motives in the Lawrence case," the report says.

After the Macpherson report was published in 1999, Mr Putnam, who was jailed for his own, separate corruption offences in 1998, alleged that, in the summer of 1994, Mr Davidson had admitted having a " corrupt connection" with Clifford Norris, the convicted drug-smuggling father of Stephen's murderer David.

Mr Ellison says that, while independent corroboration of Mr Putnam's allegation does not currently exist, there are " outstanding lines of inquiry" that could be investigated, which may change that assessment.

The barrister adds that "it is not impossible to envisage that the inquiry might have been driven to the conclusion that there must have been more to John Davidson's failure to develop information and evidence in the Lawrence investigation than simply an inappropriate manner and unfortunate unconscious racism".

Assuming Mr Putnam is available and willing to give evidence, there are reasonable grounds for suspecting that Mr Davidson acted corruptly, the findings said.

Mr Ellison's report adds: "Other than Mr Putnam's potential evidence, the material available which suggests that Mr Davidson may have been corrupt in the Stephen Lawrence investigation remains 'intelligence' and not 'evidence'."

In addition, Mr Ellison said his review has not been able to uncover all material evidence relating to the issue of corruption, adding that it is clear there are "significant areas" where relevant Metropolitan Police records should exist but cannot be found.

The original anti-corruption intelligence database itself cannot be accounted for, the report adds.

Considering whether a further public inquiry should be held, Mr Ellison said the potential for any such inquiry to discover more than his own review has may well be "limited".

"Fundamentally this is because of the chaotic state of the historical records held by the Metropolitan Police Service," he added.

Judge-led review

A judge-led public inquiry is to be launched into the work of undercover officers in the wake of the "profoundly shocking" findings.

In his review, Mark Ellison QC found that a Met Police "spy" was working within the "Lawrence family camp" during the course of the judicial inquiry into matters arising from Stephen's death.

The undercover officer in question, who is unnamed in the report, was deployed by the Special Demonstration Squad (SDS), a unit that has been at the heart of a wide range of allegations and will now be subject to a public inquiry.

In a review labelled "deeply troubling" by the Home Secretary, Mr Ellison said there is evidence to suspect one of the detectives on the original Stephen Lawrence murder investigation - detective sergeant John Davidson - acted corruptly.

Last June, former SDS officer Peter Francis claimed he had been deployed undercover from September 1993 and tasked to find out any intelligence that might be used to "smear" or undermine the Lawrence family campaign.

As a result, Mr Ellison's terms of reference were extended, and Operation Herne, an existing police investigation into the activities of the SDS supervised by Mick Creedon, chief constable of Derbyshire, agreed to prioritise "Lawrence-related" aspects of its work.

The SDS, a top secret squad within Special Branch which was operational from 1968 to 2006, focused on infiltrating campaign groups with the potential for public disorder, such as environmental and animal rights activists.

Undercover officers were deployed by the SDS into activist groups that then sought to attach themselves to the Lawrence's family's campaign to challenge the adequacy of the investigation into Stephen's murder.

Mr Ellison said: " The mere presence of an undercover Metropolitan Police officer in the wider Lawrence family camp in such circumstances is highly questionable in terms of the appearance it creates of the MPS having a spy in the family's camp."

The undercover officer in question - referred to as N81 - was also found to have held a meeting with acting Detective Inspector Richard Walton, who had been seconded to the Metropolitan Police Service (MPS) Lawrence review team, responsible for making submissions to the Macpherson inquiry.

Mr Ellison branded this meeting "a completely improper use" of knowledge gained by the deployment of N81.

"We find the opening of such a channel of communication at that time to have been 'wrong-headed and inappropriate'," Mr Ellison added.

However, Mr Ellison said he and his review team were not able to make any "definitive findings" concerning Mr Francis's claims and a public inquiry might be better placed to do so.

The review firmly concludes that information regarding undercover policing was withheld from the Macpherson inquiry.

The QC added that he felt "bound" to flag concerns about the wider implications of the findings on SDS activities - namely that the way in which the unit operated could have ultimately tainted criminal proceedings.

Mr Ellison said the nature of undercover work placed serving officers inside groups of activists who came into conflict with the police and faced arrest and prosecution.

He added: "Having a system whereby that activity was shrouded in almost total secrecy and the role of, and intelligence gained by, the undercover officer was not considered in relation to the prosecution's duty of disclosure in criminal proceedings must, in our assessment, produce the potential for there to have been unfairness in some of those proceedings."

Mr Ellison found that both the Independent Police Complaints Commission 2006 report into corruption allegations and the Metropolitan Police?s own review in 2012 were inadequate.

He added that Scotland Yard's record-keeping on its own investigations into police corruption are a cause of concern with key evidence the subject of mass shredding in 2003.

And a hard drive containing relevant data was only discovered in November 2013 after more than a year of searching for it.

Addressing the House of Commons, the Home Secretary said: "The totality of what the report shows is deeply troubling."

Referring to Mr Ellison's comments on the work of the SDS, Mrs May said: "This meant that the SDS operated as if exempt from the proper rules of disclosure in criminal cases.

"And this means there is a real potential for miscarriages of justice to have occurred."

"In particular, Ellison says there is an inevitable potential for SDS officers to have been viewed by those they infiltrated as encouraging, and participating in, criminal behaviour," she added.

Officers in criminal trials failing to reveal their true identities and failing to correct evidence given in court which they knew was wrong meant people could have been convicted for offences when they should not have been, Mrs May warned.

"We must therefore establish if there have been miscarriages of justice," she said.

Mr Ellison will now lead a further review to identify specific cases affected, assisted by the Crown Prosecution Service (CPS) and Attorney General, she said.

Announcing a public inquiry into the work of the SDS and undercover officers, Mrs May said: "The picture which emerges about the SDS from this report, and from other material in the public domain, is of significant failings of judgment, intrusive supervision and leadership over a sustained period."

She added: "I don't say this lightly, but I think that the greatest possible scrutiny is now needed into what has taken place. And so, given the gravity of what now been uncovered, I have decided that a public inquiry, led by a judge, is necessary to investigate undercover policing and the operation of the SDS."

Mrs May announced that she would bring in new legislation to create a specific offence of police corruption, to replace current "outdated" misconduct in public office.