"and then and only then does the prosecution"
Where exactly does the law state that? There's no "then and only then" or similar even written there, this is an assumption you've made up to try and align your incorrect understanding of RIPA with what's actually written. The rest of your rant is therefore irrelevant because it's based on a mis-reading of the law, and insertion of a clause that just is not there. You're effectively parroting the Daily Mail esque FUD that The Register has spouted over the years, and ultimately that's the problem with reading The Register, it'll let you be about as informed as someone who gets all their news from Fox.
This is the same publication after all that was claiming the Eurofighter had no air to ground capability whilst it was actually blowing up tanks in Libya. Yes. Really.
Now read the news Statesman article you linked to,where you claim someone quite plausibly forgot his password, I quote:
"Evidence showed that the defendant admitted in police interviews that he had set an encrypted password of between 40 and 50 characters containing both letters and numbers using an encryption software programme and that he had had originally relied on his memory to recall it but could not recall it when he was served with the notice.
The jury heard both the prosecution and defence case and accepted the prosecution case that the defendant must have kept a record of this very complex password, rather than relying on memory"
So again we're talking about someone stupid enough to incriminate himself, he admitted he had set the password, he admitted he knew the length and consistency but could not even begin to take a stab at what it was. Hence, the jury found his story to simply not be plausible. You have to keep in mind that in such trials a combination of things are taken into account that are not ever recorded in reports on it - if someone keeps changing their story this may not be mentioned but it's enough for the jury to take into account to reach a beyond reasonable doubt conclusion.
Worse, even the CPS themselves highlight that your earlier interpretation of the law is wrong:
"As the defendant claimed to have forgotten a password that he had previously memorised, it was for the prosecution to rebut this and to prove beyond all reasonable doubt that this was not the reason for the defendant failing to disclose it."
Note that they themselves accept that it's upto the prosecution to prove beyond reasonable doubt that he hadn't simply forgotten it. Something they must hence have achieved to obtain the conviction.
This is a far cry from simply saying "I've no idea what it is I never set it", or simply "I forgot it". As I said, no such case to date has ever happened - all convictions have been based on the stupidity of self incrimination and why? Because guess what, a lot of criminals crack under cross-examination and that's one of the key methods juries and judges use in determining cases.
So to jump to the conclusion he genuinely forgot it and is a victim of injustice is complete nonsense. You claim the judge must have been corrupt, okay, sure, so why didn't he appeal to get another judge? It's not like this is the US where he wouldn't have been able to afford representation, he'd have got full legal aid in 2009.