The Regulation of Investigatory Powers Act has been out of the cyber rights limelight for a while but it is worth noting that part III of the act came into force at the beginning of the month. Richard Clayton explains much better than I can:
"The commencement order means that as of October 1st a section 49 notice can be served which requires that encrypted data be “put into an intelligible form” (what you and I might call “decrypted”). Extended forms of such a notice may, under the provisions of s51, require you to hand over your decryption key, and/or under s54 include a “no tipping off” provision.
If you fail to comply with a notice (or breach a tipping off requirement by telling someone about it) then you will have committed an offence, for which the maximum penalty is two years and a fine or both. It’s five years for “tipping off” and also five years (an amendment in s15 of the Terrorism Act 2006) if the case relates to “national security”.
By convention, laws in the UK very seldom have retrospective effect, so that if you do something today, Parliament is very loth to pass a law tomorrow to make your actions illegal. However, the offences in Part III relate to failing to obey a s49 notice and that notice could be served on you tomorrow (or thereafter), but the material may have been encrypted by you today (or before).
Potentially therefore, the police could start demanding the putting into an intelligible form, not only of information that they seize in a raid tomorrow morning, but also of material that they seized weeks, months or years ago...
There are some defences in the statute to failing to comply with a notice — one of which is that you can claim to have forgotten the decryption key (in practice, the passphrase under which the key is stored). In such a case the prosecution (the burden of proof was amended during the passage of the Bill) must show beyond a reasonable doubt that you have not forgotten it. Since they can’t mind-read, the expectation must be that they would attempt to show regular usage of the passphrase, and invite the jury to conclude that the forgetting has been faked — and this might be hard to manage if a hard disk has been in a police evidence store for over a decade."
See the original for links.