Internet Movie database lists three series composers, Robert Mellin, Gian Piero Reverberi and Georges Van Parys. A reviewer, Rob Neal, writes:
It is also worth noting that the haunting score is also now available in an expanded CD from Silva Screen. The original soundtrack was in mono, but it seems there was such a demand for this piece, that the composers recently recreated a medley with a full orchestra in stereo.This was another of those series that the ABC used to show in the afternoons during school holidays. Sir Francis Drake was another: I wrote about it (and its equally haunting theme) last year.
[Soundtrack and series DVD at Amazon.co.uk]