Re:European Union dedicated questionnaire on the Encryption ...
by polymatter on Sunday November 27, 2016 @02:21PM
(#13050856)
The Register reported a man getting 13 months (http://www.theregister.co.uk/2009/11/24/ripa_jfl?page=1) - though I couldn't find a better reference.
BBC also reported on a teenager getting 16 weeks (http://www.bbc.co.uk/news/uk-england-11479831).
In both cases it seems they were jailed purely for failure to disclose passwords and not in conjunction with any other offence.
He got an additional four months for the failure to disclose the passphrase, on top of five years three months for Terrorism Act offences.