I've been recently downloading PuTTY from the official page and I have noticed a message stating:
LEGAL WARNING: Use of PuTTY, PSCP, PSFTP and Plink is illegal in countries where encryption is outlawed. I believe it is legal to use PuTTY, PSCP, PSFTP and Plink in England and Wales and in many other countries, but I am not a lawyer and so if in doubt you should seek legal advice before downloading it.
The same website then points at a website called cryptolaw.org which explains a bit more, in particular the Regulation of Investigatory Powers Act 2000.
The explanation makes sense, however some people go even further by making claims like the following: In the UK you will go to jail not just for encryption but for astronomical noise too. The author of this claim, Rick Falkvinge (founder of the Swedish Pirate Party), explains further that "you’re going to be sent to jail for an inability to unlock something that the police think is encrypted":
(...) So imagine your reaction when the police confiscate your entire collection of vacation photos, claim that your vacation photos contain hidden encrypted messages (which they don’t), and sends you off to jail for five years for being unable to supply the decryption key?
I guess my full question would be "Can the police put you in jail by simply stating that they think your data contains encrypted data and you refuse to disclose it?"