"Encrypted" could mean that's how they'll be delivered to the UK.
Or it could be a definition of the set of which messages are in question. The set is defined as the ones that users expected were supposed to be protected by encryption (or that government could not access because of encryption).
In other words, from the phrasing alone, it's not clear whether "encrypted" describes the state of the messages or the scope of the sharing.
"Encrypted" could mean that's how they'll be delivered to the UK.
Or it could be a definition of the set of which messages are in question. The set is defined as the ones that users expected were supposed to be protected by encryption (or that government could not access because of encryption).
In other words, from the phrasing alone, it's not clear whether "encrypted" describes the state of the messages or the scope of the sharing.