We have 'RIPA', the Regulation of Investigatory Powers Act 2000 containing the scary "Part III": Investigation of electronic data protected by encryption etc. Power to require disclosure
In plain English, it says "If you have encrypted data, and you know, or have ever known, the key to that data, you have to decrypt the data for the police when they tell you to. And you're not allowed to tell anyone the police told you to decrypt the data, if they tell you not to." The penalty is 4 years imprisonment.