Like a weary patient whose condition the doctors are having trouble diagnosing, the Metropolitan Police Service is bracing itself this weekend to begin another round of unpleasant poking, prodding and general intrusion.
This time it is an investigation, to be chaired by a QC, designed to find out why it took six years, two investigations and three trials to convict the killers of Damilola Taylor.
It will be the second time outsiders have scrutinised the handling of that case. The first was chaired by John Sentamu, now the Archbishop of York, and concluded that the initial investigation was broadly well-run but that the key witness - a girl identified as "Bromley" - was not handled well.
Behind the scenes, both Damilola investigations were also subjected to routine internal police reviews - formidable procedures involving teams of specialist officers running elaborate checks to make sure everything has been done by the book.
And that's just one murder case. Besides the big set-pieces and its own internal reviews, the Met is keeping the Independent Police Complaints Commission pretty busy: the IPCC is currently investigating no fewer than 76 complaints against it.
Sometimes, in fact, it must seem to the Met that it is the target of almost as many investigations as it itself is conducting, and you could probably say something similar about other forces around the country. It is hardly ideal, and the Met Commissioner, Sir Ian Blair, had problems of this kind in mind when he called recently for more public debate about what sort of policing the public wants.
For me, one of the underlying causes is that the police are too different and too distant from the rest of society, and that is something that could be fixed.
They have a unique career structure. It's not just that they tend to join young, stay for 30 years and retire on full pension often before the age of 50, which is strange enough, but it's also that this is pretty well the only career pattern in the police. Every officer begins in uniform, with a spell on the beat, and works his or her way up.
More than that, this one body of people does a great variety of jobs; indeed almost every job that doesn't require some rarified qualification (pathologist, accountant) or that isn't entirely backroom (IT manager, librarian, nurse). From detective to front-of-house reception to interviewer to victim liaison officer, when it comes to policing in its widest sense, they are usually all coppers from the same mould.
It is also hierarchical and militaristic. I remember the surprise of discovering, when following the Stephen Lawrence case, that the incident room was not a free-for-all of information and ideas like, say, a newspaper newsroom. Junior (but not necessarily younger) officers did their shifts and pursued their allocated "actions" or tasks with greater or lesser efficiency, while only senior officers had an overview; only they were in a position to do any thinking.
I am told things have improved, but I would be surprised if modern incident rooms normally accommodate the sort of open dialogue that is so essential to the writers of television detective dramas.
As for militaristic, I do not understand why officers of any rank ever need to wear uniform unless they have a special need to communicate to the public who they are. In some circumstances, the uniform is practical and enhances respect; in others it can be a barrier.
The world of the police in general is more unlike the world of other workers than it needs to be, and the effect is to set the police apart, both in our minds and in their own. That makes it harder for us to understand and trust them, and it also tends to make them more resentful of criticism, so the distance grows wider.
We would benefit from a more varied and shaded police service, in which people didn't necessarily join young, didn't lock themselves in for 30 years, and were far less likely to drop out at 50, when they may be at the peak of their abilities.
And instead of drawing so heavily on one pool of people recruited in a standard fashion, and then spreading them around such a variety of jobs, the service could hire and train people specifically for those jobs.
If you advertised for victim liaison officers who never had to wear uniform but enjoyed police rates of pay, you would find good people. If you advertised for trainee detectives on similar terms, you might well be swamped. And if you advertised for deputy chief constables, whose jobs are often dominated by management and strategy, you might find excellent people from other parts of the service industry.
And people could move in and out of police work much more freely, bringing ideas and new mindsets in, and taking out with them a better understanding.
Many in the police service would welcome such change, and many, sadly, would oppose it, but that's not really the point. It is our police service. We are not looking for "coppers' coppers", but for GPs' coppers, van drivers' coppers and schoolkids' coppers. The constant chain of reviews, inquiries and complaints is telling us that things are not right, so let's make them better.
Brian Cathcart is assistant editor of the New Statesman