Only one case which I've seen mention of: http://www.bbc.co.uk/news/uk-25745989
He got an additional four months for the failure to disclose the passphrase, on top of five years three months for Terrorism Act offences.
He got an additional four months for the failure to disclose the passphrase, on top of five years three months for Terrorism Act offences.
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.