When my friend Pinkie entertained Her Majesty in Wandsworth for some 18 months a few years back, he found he was the "only one in the nick who had actually committed a crime." Even though a very high proportion of residents were, of course, as guilty as hell, all of them claimed they "didn't do it". They were framed, or set up, or they were protecting someone else. Or they had received a most inadequate defence, full of flaws, which would eventually "prove" their innocence. It is such a common bleat among prisoners, that it merely tends to create big yawns, not only outside nick, but inside as well. The assumption of the entire judiciary, and often of the public, is that most convicted prisoners are going to plead innocence, however guilty they were in reality. And there are, of course, miscarriages of justice the other way round. A clever criminal who can "fix" crucial evidence, or tamper with a jury, or threaten witnesses, is quite capable of creating his very own malpractice. There is nothing at all new in that. Many hardened criminals, too, have only actually received sentences for a fraction of their crimes.

But close observers of our justice system are also very well aware that a proportion of people convicted of crimes and imprisoned should never have been so, for myriad reasons. A sloppy defence is top of the list. But recently it has been manifestly confirmed what many of us knew all along. That the police are quite capable of fabricating evidence to suit them; that lawyers are capable of gross negligence in not putting forward an infallible defence which is actually open to them at the time; or that the accused, sometimes of low intelligence or even unable to speak English, get steam-rollered by a flawed system.

There is a situation in the UK whereby widespread and continuing miscarriages of justice occur almost daily. They are all based on not just casual negligence but often get to the very heart of the infrastructure of our society. If a person is wrongly convicted it not only strikes at his or her personal liberty - serious enough by any standards - but at every last one of us. For, ultimately it is we who have created the system and we who must live or die by it.

Hitchcock's favourite "mystery gambit" was to allow the audience to know the full plot. In fact, the audience were the ONLY people who knew the full plot. And his heroes were always innocent, but being fitted up for a crime - and only we knew where it was coming from. For example, North by North West, which brought the goodies and the baddies in full pursuit. Or Rear Window where everyone but us was convinced he was fabricating. The Thirty Nine Steps was based on a similar plot in which the hero spent the whole story trying to both prove his own innocence and escape from those who thought he was guilty. These are all potential real life scenarios, but in real life there is seldom a happy ending. Only the hero knows he really didn't do it, and right to the very end no one else believes him. In the case of Hanratty, the finale was the ultimate end and resulted in the black cap and judicial murder.

The recent Bridgewater case illustrates the syndrome almost to perfection, but luckily it caught a taste of Hitchcock on the way and there might be a happy ending after all. The story of Carol Hanson is one of the saddest we have ever come across and has every ingredient of the ultimate nightmare.

You know you didn't do it, but simply no one, including your own lawyers, believes you. In Carol's case she spent more than half her life in absolute despair and misery before she could take no more and took her own hopeless life.

Each of these cases is unique in their way and, apart from Carol Hanson, they are well known to the public. But in terms of miscarriages, all three are frightening examples of what could happen to any one of us if the system we have fostered and supported, often hysterically and ignorantly, continues unquestioned. In these three cases, even after all the headlines, a proper analysis of just what went into legally perverting the course of justice, makes very disturbing reading.

Yet we are now going into a society, ironically even more so under New Labour, where police are to be given substantially more wide-ranging powers. There will soon be greater powers of interception, such as legal telephone tapping, even of conversations between a client and his lawyer; new powers of arrest; the abolition of a proper caution; the naming in a community of any person convicted of a sex crime; "Zero Tolerance" and so on. Each of these are likely to gnaw away at justice, which is already deeply flawed as these cases so adequately illustrate.

Yet all, even to the cynic, is not lost. Since all of the three cases quoted began there have been many advances in technology, particularly in forensic science which in future should be able to help both sides. DNA is singularly the most significant criminal yardstick to have emerged for it is so irrefutable. Blood no longer has to match by type alone. You can prove beyond doubt that it does so. A semen test will prove a sex offence of any calibre quite decisively. A single hair will properly identify both the victim and the assailant. Hanratty could not have been found guilty had proper DNA tests existed during his ordeal.

Then along came Electrostatic Definition Analysis (ESDA) which proved conclusively that the Bridgewater case was based on forged documents. Also in use now are taped police interviews, and video taping is clearly on the cards. That certainly would have also been a serious blow to the case against the Bridgewater Four.

Because of growing public disquiet about the whole spate of obvious miscarriages of justice, the political climate, even under the Tories, led to the Royal Commission on Criminal Justice which in turn successfully suggested the Criminal Cases Review Commission (CCRC), which in theory is an independent body tainted neither by politics, nor the established bar.

Forensic technology should lead to less suspect evidence. If evidence is still suspect, then it should lead to the CCRC.

But what can never be fully satisfied, even after any or all of the above has been exercised, is the crooked copper. The ambitious "acting" Inspector who has an axe to grind - or wants to seal his promotion. He will learn, as all crooks do, to corrupt even fail-safe evidence. He can still plant; he can still verbal; he can even create his own DNA tests if he is that determined. He can bully witnesses to make false statements, or to not appear, or he can simply destroy or ignore vital evidence he comes across merely because it does not conform to his own private theory.

There will never be a time when a miscarriage is not possible, because of human chicanery or extreme bad luck - or even through mischance or coincidence. All the cases in this file, which will continue as long as injustice in our courts survives, will show that at least sometimes justice may be seen to be done, however long it takes.

It is an accepted estimate that during any given year in the UK some 800 miscarriages of justice are perpetrated because of our present system. This is based not only on the statistics of Scallywag/Scandals, but all the legal watchdogs such as prison reform groups, Litigants in Person and so on. There are some 320 British groups linked one way or the other into monitoring the system. That is a lot of people who have run foul of it one way or the other. In the end it is only the spotlight of publicity - the opening of their cases to proper scrutiny - that gives any of them any vestige of hope.

That's why we must all keep at it.