In June 1988, a detective sergeant from the Metropolitan Police's Flying Squad had a drink with a friend at the Tiger's Head pub in Chislehurst, south-east London. His companion was a violent criminal who smuggled drugs on an industrial scale. The next day, when the customs service swooped on a consignment of cannabis freshly arrived in the country, they arrested several men, but the policeman's friend was not one of them. He escaped by car.
When this was revealed at the Macpherson Inquiry into the murder of Stephen Lawrence it drew gasps of horror, for the policeman's friend was none other than Clifford Norris, father of David Norris, then one of the prime suspects in the Lawrence murder (and since convicted of the crime). The implication was sensational: could this criminal's police connections have helped him protect his son?
It was a rare glimpse into the pit of tangled and poisonous snakes that is police corruption. That was 1998. Last week we had another, with the publication of the review by Mark Ellison QC into continuing concerns about police misconduct in the Lawrence case. His findings are shocking – revealing among other things that the Metropolitan Police was still covering up information as recently as 2012.
The Home Secretary, Theresa May, appeared to respond to Ellison with admirable firmness, but her action is not quite what it seems. On the basis of her remarks in the House of Commons it is clear that she is ordering a public inquiry into undercover policing – a matter no less grave – but the inquiry will have no brief to investigate corruption. The lid over the pit of snakes, it seems, may slide quietly back into place.
No issue caused more fury at the Macpherson Inquiry 16 years ago than Clifford Norris's police connections and their possible influence on the first, disastrous police investigation of Stephen Lawrence's murder. The Lawrences' counsel, Michael Mansfield, pressed it to the point where he seemed to accuse the inquiry panel itself of bad faith.
The chair, Sir William Macpherson, insisted he had the police under all possible pressure to come clean, while an indignant Met treated Mansfield's argument as a wild conspiracy theory, one former officer declaring it a "Merlin's broth of magic and mirrors and innuendoes and nudges".
Now we know better. The Ellison Review shows that, while Sir William and his team apparently did what they could to drag evidence out of the Met, the police held back. They made no serious effort to comply with requests to look for evidence of corruption, and important information was withheld. Astonishingly, Ellison found that from 1994 until 1998 – the years between Stephen Lawrence's murder and the inquiry – a high-powered secret operation existed to investigate corruption in the Met, but that almost all the documentation it produced was later destroyed.
He was also highly critical of a Met review of the Lawrence case conducted as recently as 2012, which not only drew a veil over destruction of evidence but also gave the false impression that a remarkable allegation against a detective on the Lawrence investigation surfaced too late to be put before the inquiry in 1998.
This was the suggestion that John Davidson, the third-ranking officer on the case, admitted to a colleague that he had received money from Clifford Norris. Ellison (who was unable to judge the truth of this) pointed out that in 2012 the Met said the allegation was made "late in 1998" – by implication after the Macpherson Inquiry ceased hearing evidence – when in fact it was made while the inquiry was sitting.
That 2012 review was, Ellison concluded witheringly, "another example of the MPS [Metropolitan Police Service] providing misleading reassurance to the family and to the public".
Police corruption, it is plain, does not spontaneously reveal itself and even after many years there is an impulse among some officers to conceal it. Yet Theresa May is now apparently ready to leave the police in charge of investigating the snakepit.
Here is what she promised on corruption in the Commons: "I have asked the director general of the National Crime Agency to consider quickly how best an investigation can be taken forward into this aspect of Mr Ellison's findings and report back to me."
Surely we are far past the point where the Home Secretary, on our behalf and on behalf of the Lawrences, should place responsibility for tackling this matter with any police officer, no matter how eminent. And it is nothing like enough to say that whatever he recommends will be reported privately to a government minister.
As Neville and Doreen Lawrence detected within days of their son's murder, aged 18, in an unprovoked attack at an Eltham bus-stop by a gang of white youths in 1993, and as Michael Mansfield made clear in 1998, that first police investigation stinks. It stinks of incompetence and racism, and the Macpherson Report exposed that. But it also stinks of corruption, and the Clifford Norris connections are only a part of that.
The Ellison Review takes us closer to the source of the smell, but only by one step, and we need to be told much more. So why is this not part of the same public inquiry as undercover policing?
Don't let anyone say it is just a matter of history. Serving police officers are subject to temptations to take money from crooks and cover up for errant colleagues in the same way that their 1980s and 1990s predecessors were. They are watching now.
If they see that we, as a society, are not ready to do whatever it takes to find the truth about corruption, they will draw one conclusion: they can do what they like, so long as they bury it deep enough.
Brian Cathcart is the author of 'The Case of Stephen Lawrence', published by Penguin