Police have released interview tapes of child abuser Vanessa George. That should worry us all.

Justice is flouted so routinely these days that you may feel they can't do anything more to shock us. And then this happens. Nursery worker Vanessa George,39, has been found guilty of abusing young children at the nursery where she worked. Given that anyone who comes within 100 yards of a child these days has to go through Criminal Records Bureau checks, you might wonder how that can happen. Well, the system seems to be wrecking scout groups, schools and after-hours clubs, who have seen a bit drop in parents volunteering to help out – innocent parents who simply can't bear the intrusion of a CRB investigation – though it doesn't seem to stop the real abusers.

Maybe, as with the Soham murders, it was just police incompetence. But even that is not the real shocker. Really shocking is that the police interview tapes with Vanessa George have been released to the BBC and are now all over the internet.

Police interview tapes came in for one reason alone. There were so many cases of defendants pleading that they had been bullied into confessions by police questioning that, to protect the public against any possibility of police abuse, it was ruled that all police interviews should be taped. It would also ensure that what appeared as evidence in court was properly extracted and did actually correspond to what a defendant said.

Now interviews are conducted on video, not just audio. A relief to innocent people who are accused of things they didn't do, you might think. Until you find that the police are releasing your tapes to the BBC, as they did in this case – complete, of course, with their own commentary: "She clearly knows what she did was wrong..." and "She was still trying to manipulate the situation..." etc etc. Yes, she's guilty, yes, she's going to jail, and good thing too. But the duty of the police is to prosecute cases, not to put their own spin on them. Something brought in to protect the public is now being used for police PR.

It's truly amazing. How are the police going to get anyone to confess to anything if they imagine that edited snippets of their tapes are going to be splattered all over the BBC and the internet? I've often said that if you are arrested by the police, the best thing to do is to say absolutely nothing. Yes, they will hold you as long as they can out of spite, but at least you won't be set up, and the BBC won't be playing tapes of you saying something unfortunate for the next twenty years. Just because Vanessa George has been found guilty doesn't make it any better. Today it's tapes of guilty people. Soon it will be tapes of anyone they pull in, plus commentary, if they figure that a bit of public outrage might help the case against them. You might think the rules of natural justice mean that could not possibly happen. But seeing how far our liberties have been eroded, it's surely only a matter of time.

Dr Butler's book The Rotten State of Britain is now in paperback.