That reminded me of a TV show I saw:
I recall seeing a Law and Order episode that pointed out that the double jeopardy protection in the US constitution isn't absolute. The example was a trial where the judge was corrupt, I believe. That defendant could be tried again because he never had a "real" trial in the first place. This exception, however, just emphasized the unusual circumstances that have to occur to justify disregarding this protection. The "new and compelling evidence" standard that now appears to be in place in Britain sets a much lower hurdle. Sometimes there is such a thing as a "slippery slope".