I think the double jeopardy law doesn't exist in the UK anymore. It was a stupid bloody law to be honest. The fact you could be found innocent of a crime, and then admit you committed it after the verdict (without being able to be tried again) was just about the most ridiculous law I ever heard of.
I think I heard something about it in reference to the Stephen Lawrence case, a couple of years or so back?. I'm no legal expert so I wasn't sure how that would work in a case like the one Rantzen mention, if the defendant could be brought back to trial at a later date, if the witness decided they wanted to testify when their older for example. It must be awful for them when they realise that the accused was let free because they were so upset over the proceedings, that could lead to feelings of guilt etc. - awful.