This is the best comment really... I brought up Truecrypt's Hidden OS feature a while ago (here: http://news.ycombinator.com/item?id=3415658 ) and apparently in the UK you have to somehow prove the non-existence of such a thing. If you can't get them to leave you alone through such above trickery it becomes a fairly simple calculated choice deciding whether obstruction of justice is a less harmful penalty than what they want to find and charge you for after decryption.