Moreover you give a (wrong) password and it doesn't work. You say "I am pretty sure that was right, to the best of my knowledge. I suppose I could have gotten it wrong, or maybe even the drive is damaged....." How do they know that this is a deliberate act? It seems here that lying to the police suddenly gives some degree of protection which strikes me as somewhat insane.
Indeed there have been cases in the UK where the defendant's apparent cooperation was enough to ensure there could be no RIPA prosecution even though the password to the encrypted hard drive did not seem to work. So this is not merely hypothetical.