Imagine for a moment that Mark Kennedy, the police spy who spent seven years undercover in the environmental movement, had not been unmasked by activists?

If he had remained concealed, there would have no cascade of disclosures about his espionage. And there would in turn have been no revelations about the other undercover officers at the heart of the police's 40-year operation to infiltrate and disrupt political campaigns.

More specifically, 20 activists who were convicted over the plan to occupy the Ratcliffe-on-Soar power station would not have had their convictions overturned.

Three appeal court judges ruled that their convictions were unsafe because crucial surveillance tapes recorded by Kennedy had been withheld from them.

Another six activists could also have been unjustly convicted if prosecutors had not abandoned their trial after Kennedy had been unmasked.

The miscarriage of justice over the Ratcliffe trial only became evident because Kennedy was by chance outed.

But the question here is - how many other activists have been wrongly convicted because the involvement of police spies has remained hidden? How many other times have police and prosecutors sat on key evidence gathered by an undercover police officer which could have cleared campaigners?

At the moment, we simply don't know. Perhaps you could help us find out about other cases?

The police clearly have no interest in shedding any light on their secret operations. More controversially, Keir Starmer, the director of public prosecutions, has decided that there is no need to delve further into this question.

Starmer says that he will only do anything if allegations are brought to him by members of the public.

Conveniently this throws the onus onto the members of the public who are inevitably stymied as they do not know where the undercover police officers have been operating. Those outside the police and the Crown Prosecution Service don't know where to look.

Last week saw the publication of the last inquiry into the failure to hand over the Kennedy tapes to the activists' lawyers, Bindmans.

A few things have now become clearer. No prosecutors or police officers are to be disciplined over the miscarriage of justice in the Ratcliffe case. The only disciplinary inquiry against a prosecutor (Ian Cunningham) was dropped after he retired.

There was a sprinkling of criticism over the conduct of police officers, but none serious enough to result in any charges of misconduct.

There have been at least five inquiries - all private - into the withholding of the Kennedy tapes, but in the end, it has been unsatisfactory for those seeking answers, to put it mildly.

The two inquiries which were published do little to explain why the Kennedy tapes were withheld and what were the motivations of the police and prosecutors.

What these inquiries do reveal is a blow-by-blow account of a bureaucratic battle between the police and the Crown Prosecution Service to avoid being blamed.

In mind-numbing detail, the two inquiries set out the claims of the police and the prosecutors.

As last week's report from the Independent Police Complaints Commission diplomatically comments, "It must be noted that there are a number of conflicting accounts surrounding what documentation was handled, by whom and when".