Attempts to Commit Offences
Voluntarily concealing (including via encryption or information-hiding tools) a known design to commit a death/life-imprisonment offence, or falsely representing facts about such a design, intending or knowing it will likely facilitate that offence, is punished with up to 7 years' imprisonment (if the offence is committed) or up to 3 years plus fine (if not).
This specifically criminalises concealing knowledge of a planned serious crime in order to help it succeed - and importantly, explicitly covers using encryption or digital information-hiding tools to conceal such knowledge, a modern addition reflecting how criminal concealment increasingly happens through technology.
Someone who knows about a planned serious crime and uses encrypted messaging specifically to hide evidence of that knowledge from investigators, intending to help the crime succeed, can be prosecuted under this section - the explicit reference to encryption tools reflects the digital-age update from the old IPC.