The Mk III and Mk IV are probably the most common Copicats seen these days. I suspect this may possibly because more of them were sold. It was distributed in the USA under the “Guild” name although, as you can see from the pic. further down this page, some UK 240 volt models were also labelled as “Guild”. It was also distributed in some parts of Europe under the “Kent” brand name.
The first solid state Mk III Copicats appeared around 1965 and the Mk IV Copicats appear in catalogues up to around 1977.
There are various differences between the Mk III and the Mk IV. The Mk III had twin pointer knobs whereas the Mk IV had round knobs. Also, the voltage selector which appears next to the fuse holder, is on the Mk III but was omitted on the Mk IV. Later Mk IIIs had the motor bolts parallel to the casing but they were at a slight angle on earlier models.
Sadly, a lot of Mk IVs were modified with extra sockets drilled into the front panel for a footswitch or extra input.
Based on the info I’ve been given, I believe the following pic of my current Copicat indicates that it is an early Mk III, probably from the late 1960s or very early 1970s.
The following pic. shows the Mk IV but with the Guild logo.