the English OPD, or its Australian rebadging, the Telecom Computerphone?
Well, my father worked for ICL (the English-based company that did the box with Sinclair), so it could've been either. I've got a vague feeling it was the Telecom-badged one, though. We even (eventually) got a colour screen for it.
My first days of BBSing were on this thing (300bps, or 1200/75), too.
http://www.nvg.ntnu.no/sinclair/computers/clones/opd.htm
we had one of these OPD things (as well as two Spectrums, of course). ah, the 80's...