Are there any differences in how privilege operates in civil, criminal, regulatory or investigatory situations?
The privilege (the lawyers' duty of professional secrecy) operates in the same way, irrespective of the field in which it may be applicable.
Can notes of interviews with employees and other documents produced during investigations be covered by privilege?
If the notes are taken by an external lawyer, those notes and any other information or documents produced during the meeting are covered by legal professional privilege. In any other circumstance, those notes and documents can be used in court if they were seized during a search, unless it can be proven than they were drawn up or gathered with the sole aim of seeking legal advice from an external lawyer.
The defendant cannot be forced to show or submit those notes and documents if they could be self-incriminating.