@signalapp Issue clause seems to be 98(4):
"(4) A person commits an offence if, in response to an information notice, the
person—
(a) provides information which is encrypted such that it is not possible for OFCOM to understand it, or produces a document which is encrypted such that it is not possible for OFCOM to understand the information it contains, and
(b) the person’s intention was to prevent OFCOM from understanding such information."
https://bills.parliament.uk/publications/49376/documents/2822