(a) does copyright infringement fall under criminal, civil or common law?
(b) was it different prior to the 1988 Act?
(c) or does/did it all depend upon the nature of the infringement/offence?
Hello again... and many thanks for your kind words.
It can be either, and basically depends on the infringement.
Most commonly copyright is dealt with under civil proceedings. I.e. the copyright owner may take action to prevent the infringement (such as an injunction), or claim damages for lost income/royalties/etc.
Cases such as large scale counterfeiting would typically be dealt with by the police under criminal proceedings.