This unique set appears to be one of the 165 preproduction sets made by Collier and Beale.
It has some differences compared to standard production units. The main points of difference are the simple dial clamps fitted, and that the case has no carry handles or key slides. However brackets to hold a carry strap of leather or webbing are fitted.
Other differences on this set are the fitting of a third terminal below the 12 Volt input terminals. This is of a later design so is likely a modification made after the sets manufacture. A second difference is what appears to be a push button fitted just above the netting switch. It is impossible to tell from a photograph if this is original but as it is unlabeled it was most likely fitted at a later date. It is also probable that the square meter is a later replacement although it may just be what was available at the time of manufacture of the set.